Re: [PATCH v3 25/77] ncr5380: Rework disconnect versus poll logic
On 12/22/2015 02:18 AM, Finn Thain wrote:
The atari_NCR5380.c and NCR5380.c core drivers differ in their handling of
target disconnection. This is partly because atari_NCR5380.c had all of
the polling and sleeping removed to become entirely interrupt-driven, and
it is partly because of damage done to NCR5380.c after atari_NCR5380.c was
forked. See commit 37cd23b44929 ("Linux 2.1.105") in history/history.git.
The polling changes that were made in v2.1.105 are questionable at best:
if REQ is not already asserted when NCR5380_transfer_pio() is invoked, and
if the expected phase is DATA IN or DATA OUT, the function will schedule
main() to execute after USLEEP_SLEEP jiffies and then return. The problems
here are the expected REQ timing and the sleep interval*. Avoid this issue
by using NCR5380_poll_politely() instead of scheduling main().
The atari_NCR5380.c core driver requires the use of the chip interrupt and
always permits target disconnection. It sets the cmd->device->disconnect
flag when a device disconnects, but never tests this flag.
The NCR5380.c core driver permits disconnection only when
instance->irq != NO_IRQ. It sets the cmd->device->disconnect flag when
a device disconnects and it tests this flag in a couple of places:
1. During NCR5380_information_transfer(), following COMMAND OUT phase,
if !cmd->device->disconnect, the initiator will take a guess as to
whether or not the target will then choose to go to MESSAGE IN phase
and disconnect. If the driver guesses "yes", it will schedule main()
to execute after USLEEP_SLEEP jiffies and then return there.
Unfortunately the driver may guess "yes" even after it has denied
the target the disconnection privilege. When the target does not
disconnect, the sleep can be beneficial, assuming the sleep interval
is appropriate (mostly it is not*).
And even if the driver guesses "yes" correctly, and the target would
then disconnect, the driver still has to go through the MESSAGE IN
phase in order to get to BUS FREE phase. The main loop can do nothing
useful until BUS FREE, and sleeping just delays the phase transition.
2. If !cmd->device->disconnect and REQ is not already asserted when
NCR5380_information_transfer() is invoked, the function polls for REQ
for USLEEP_POLL jiffies. If REQ is not asserted, it then schedules
main() to execute after USLEEP_SLEEP jiffies and returns.
The idea is apparently to yeild the CPU while waiting for REQ.
This is conditional upon !cmd->device->disconnect, but there seems
to be no rhyme or reason for that. For example, the flag may be
unset because disconnection privilege was denied because the driver
has no IRQ. Or the flag may be unset because the device has never
needed to disconnect before. Or if the flag is set, disconnection
may have no relevance to the present bus phase.
Another deficiency of the existing algorithm is as follows. When the
driver has no IRQ, it prevents disconnection, and generally polls and
sleeps more than it would normally. Now, if the driver is going to poll
anyway, why not allow the target to disconnect? That way the driver can do
something useful with the bus instead of polling unproductively!
Avoid this pointless latency, complexity and guesswork by using
NCR5380_poll_politely() instead of scheduling main().
* For g_NCR5380, the time intervals for USLEEP_SLEEP and USLEEP_POLL are
200 ms and 10 ms, respectively. They are 20 ms and 200 ms respectively
for the other NCR5380 drivers. There doesn't seem to be any reason for
this discrepancy. The timing seems to have no relation to the type of
adapter. Bizarrely, the timing in g_NCR5380 seems to relate only to one
particular type of target device. This patch attempts to solve the
problem for all NCR5380 drivers and all target devices.
Signed-off-by: Finn Thain
---
drivers/scsi/NCR5380.c | 137
++-
drivers/scsi/NCR5380.h | 11 ---
drivers/scsi/atari_NCR5380.c | 24 ++-
drivers/scsi/g_NCR5380.c |4 -
4 files changed, 15 insertions(+), 161 deletions(-)
Reviewed-by: Hannes Reinecke
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
h...@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[PATCH v3 25/77] ncr5380: Rework disconnect versus poll logic
The atari_NCR5380.c and NCR5380.c core drivers differ in their handling of
target disconnection. This is partly because atari_NCR5380.c had all of
the polling and sleeping removed to become entirely interrupt-driven, and
it is partly because of damage done to NCR5380.c after atari_NCR5380.c was
forked. See commit 37cd23b44929 ("Linux 2.1.105") in history/history.git.
The polling changes that were made in v2.1.105 are questionable at best:
if REQ is not already asserted when NCR5380_transfer_pio() is invoked, and
if the expected phase is DATA IN or DATA OUT, the function will schedule
main() to execute after USLEEP_SLEEP jiffies and then return. The problems
here are the expected REQ timing and the sleep interval*. Avoid this issue
by using NCR5380_poll_politely() instead of scheduling main().
The atari_NCR5380.c core driver requires the use of the chip interrupt and
always permits target disconnection. It sets the cmd->device->disconnect
flag when a device disconnects, but never tests this flag.
The NCR5380.c core driver permits disconnection only when
instance->irq != NO_IRQ. It sets the cmd->device->disconnect flag when
a device disconnects and it tests this flag in a couple of places:
1. During NCR5380_information_transfer(), following COMMAND OUT phase,
if !cmd->device->disconnect, the initiator will take a guess as to
whether or not the target will then choose to go to MESSAGE IN phase
and disconnect. If the driver guesses "yes", it will schedule main()
to execute after USLEEP_SLEEP jiffies and then return there.
Unfortunately the driver may guess "yes" even after it has denied
the target the disconnection privilege. When the target does not
disconnect, the sleep can be beneficial, assuming the sleep interval
is appropriate (mostly it is not*).
And even if the driver guesses "yes" correctly, and the target would
then disconnect, the driver still has to go through the MESSAGE IN
phase in order to get to BUS FREE phase. The main loop can do nothing
useful until BUS FREE, and sleeping just delays the phase transition.
2. If !cmd->device->disconnect and REQ is not already asserted when
NCR5380_information_transfer() is invoked, the function polls for REQ
for USLEEP_POLL jiffies. If REQ is not asserted, it then schedules
main() to execute after USLEEP_SLEEP jiffies and returns.
The idea is apparently to yeild the CPU while waiting for REQ.
This is conditional upon !cmd->device->disconnect, but there seems
to be no rhyme or reason for that. For example, the flag may be
unset because disconnection privilege was denied because the driver
has no IRQ. Or the flag may be unset because the device has never
needed to disconnect before. Or if the flag is set, disconnection
may have no relevance to the present bus phase.
Another deficiency of the existing algorithm is as follows. When the
driver has no IRQ, it prevents disconnection, and generally polls and
sleeps more than it would normally. Now, if the driver is going to poll
anyway, why not allow the target to disconnect? That way the driver can do
something useful with the bus instead of polling unproductively!
Avoid this pointless latency, complexity and guesswork by using
NCR5380_poll_politely() instead of scheduling main().
* For g_NCR5380, the time intervals for USLEEP_SLEEP and USLEEP_POLL are
200 ms and 10 ms, respectively. They are 20 ms and 200 ms respectively
for the other NCR5380 drivers. There doesn't seem to be any reason for
this discrepancy. The timing seems to have no relation to the type of
adapter. Bizarrely, the timing in g_NCR5380 seems to relate only to one
particular type of target device. This patch attempts to solve the
problem for all NCR5380 drivers and all target devices.
Signed-off-by: Finn Thain
---
drivers/scsi/NCR5380.c | 137 ++-
drivers/scsi/NCR5380.h | 11 ---
drivers/scsi/atari_NCR5380.c | 24 ++-
drivers/scsi/g_NCR5380.c |4 -
4 files changed, 15 insertions(+), 161 deletions(-)
Index: linux/drivers/scsi/NCR5380.c
===
--- linux.orig/drivers/scsi/NCR5380.c 2015-12-22 12:16:07.0 +1100
+++ linux/drivers/scsi/NCR5380.c2015-12-22 12:16:10.0 +1100
@@ -139,17 +139,7 @@
* piece of hardware that requires you to sit in a loop polling for
* the REQ signal as long as you are connected. Some devices are
* brain dead (ie, many TEXEL CD ROM drives) and won't disconnect
- * while doing long seek operations.
- *
- * The workaround for this is to keep track of devices that have
- * disconnected. If the device hasn't disconnected, for commands that
- * should disconnect, we do something like
- *
- * while (!REQ is asserted) { sleep for N usecs; poll for M usecs }
- *
- * Some tweaking of N and M needs to be done. An algorithm based
- * on "time to data" would give the best results
[PATCH v3 25/77] ncr5380: Rework disconnect versus poll logic
The atari_NCR5380.c and NCR5380.c core drivers differ in their handling of
target disconnection. This is partly because atari_NCR5380.c had all of
the polling and sleeping removed to become entirely interrupt-driven, and
it is partly because of damage done to NCR5380.c after atari_NCR5380.c was
forked. See commit 37cd23b44929 ("Linux 2.1.105") in history/history.git.
The polling changes that were made in v2.1.105 are questionable at best:
if REQ is not already asserted when NCR5380_transfer_pio() is invoked, and
if the expected phase is DATA IN or DATA OUT, the function will schedule
main() to execute after USLEEP_SLEEP jiffies and then return. The problems
here are the expected REQ timing and the sleep interval*. Avoid this issue
by using NCR5380_poll_politely() instead of scheduling main().
The atari_NCR5380.c core driver requires the use of the chip interrupt and
always permits target disconnection. It sets the cmd->device->disconnect
flag when a device disconnects, but never tests this flag.
The NCR5380.c core driver permits disconnection only when
instance->irq != NO_IRQ. It sets the cmd->device->disconnect flag when
a device disconnects and it tests this flag in a couple of places:
1. During NCR5380_information_transfer(), following COMMAND OUT phase,
if !cmd->device->disconnect, the initiator will take a guess as to
whether or not the target will then choose to go to MESSAGE IN phase
and disconnect. If the driver guesses "yes", it will schedule main()
to execute after USLEEP_SLEEP jiffies and then return there.
Unfortunately the driver may guess "yes" even after it has denied
the target the disconnection privilege. When the target does not
disconnect, the sleep can be beneficial, assuming the sleep interval
is appropriate (mostly it is not*).
And even if the driver guesses "yes" correctly, and the target would
then disconnect, the driver still has to go through the MESSAGE IN
phase in order to get to BUS FREE phase. The main loop can do nothing
useful until BUS FREE, and sleeping just delays the phase transition.
2. If !cmd->device->disconnect and REQ is not already asserted when
NCR5380_information_transfer() is invoked, the function polls for REQ
for USLEEP_POLL jiffies. If REQ is not asserted, it then schedules
main() to execute after USLEEP_SLEEP jiffies and returns.
The idea is apparently to yeild the CPU while waiting for REQ.
This is conditional upon !cmd->device->disconnect, but there seems
to be no rhyme or reason for that. For example, the flag may be
unset because disconnection privilege was denied because the driver
has no IRQ. Or the flag may be unset because the device has never
needed to disconnect before. Or if the flag is set, disconnection
may have no relevance to the present bus phase.
Another deficiency of the existing algorithm is as follows. When the
driver has no IRQ, it prevents disconnection, and generally polls and
sleeps more than it would normally. Now, if the driver is going to poll
anyway, why not allow the target to disconnect? That way the driver can do
something useful with the bus instead of polling unproductively!
Avoid this pointless latency, complexity and guesswork by using
NCR5380_poll_politely() instead of scheduling main().
* For g_NCR5380, the time intervals for USLEEP_SLEEP and USLEEP_POLL are
200 ms and 10 ms, respectively. They are 20 ms and 200 ms respectively
for the other NCR5380 drivers. There doesn't seem to be any reason for
this discrepancy. The timing seems to have no relation to the type of
adapter. Bizarrely, the timing in g_NCR5380 seems to relate only to one
particular type of target device. This patch attempts to solve the
problem for all NCR5380 drivers and all target devices.
Signed-off-by: Finn Thain
---
drivers/scsi/NCR5380.c | 137 ++-
drivers/scsi/NCR5380.h | 11 ---
drivers/scsi/atari_NCR5380.c | 24 ++-
drivers/scsi/g_NCR5380.c |4 -
4 files changed, 15 insertions(+), 161 deletions(-)
Index: linux/drivers/scsi/NCR5380.c
===
--- linux.orig/drivers/scsi/NCR5380.c 2015-12-22 12:16:07.0 +1100
+++ linux/drivers/scsi/NCR5380.c2015-12-22 12:16:10.0 +1100
@@ -139,17 +139,7 @@
* piece of hardware that requires you to sit in a loop polling for
* the REQ signal as long as you are connected. Some devices are
* brain dead (ie, many TEXEL CD ROM drives) and won't disconnect
- * while doing long seek operations.
- *
- * The workaround for this is to keep track of devices that have
- * disconnected. If the device hasn't disconnected, for commands that
- * should disconnect, we do something like
- *
- * while (!REQ is asserted) { sleep for N usecs; poll for M usecs }
- *
- * Some tweaking of N and M needs to be done. An algorithm based
- * on "time to data"
Re: [PATCH v3 25/77] ncr5380: Rework disconnect versus poll logic
On 12/22/2015 02:18 AM, Finn Thain wrote:
The atari_NCR5380.c and NCR5380.c core drivers differ in their handling of
target disconnection. This is partly because atari_NCR5380.c had all of
the polling and sleeping removed to become entirely interrupt-driven, and
it is partly because of damage done to NCR5380.c after atari_NCR5380.c was
forked. See commit 37cd23b44929 ("Linux 2.1.105") in history/history.git.
The polling changes that were made in v2.1.105 are questionable at best:
if REQ is not already asserted when NCR5380_transfer_pio() is invoked, and
if the expected phase is DATA IN or DATA OUT, the function will schedule
main() to execute after USLEEP_SLEEP jiffies and then return. The problems
here are the expected REQ timing and the sleep interval*. Avoid this issue
by using NCR5380_poll_politely() instead of scheduling main().
The atari_NCR5380.c core driver requires the use of the chip interrupt and
always permits target disconnection. It sets the cmd->device->disconnect
flag when a device disconnects, but never tests this flag.
The NCR5380.c core driver permits disconnection only when
instance->irq != NO_IRQ. It sets the cmd->device->disconnect flag when
a device disconnects and it tests this flag in a couple of places:
1. During NCR5380_information_transfer(), following COMMAND OUT phase,
if !cmd->device->disconnect, the initiator will take a guess as to
whether or not the target will then choose to go to MESSAGE IN phase
and disconnect. If the driver guesses "yes", it will schedule main()
to execute after USLEEP_SLEEP jiffies and then return there.
Unfortunately the driver may guess "yes" even after it has denied
the target the disconnection privilege. When the target does not
disconnect, the sleep can be beneficial, assuming the sleep interval
is appropriate (mostly it is not*).
And even if the driver guesses "yes" correctly, and the target would
then disconnect, the driver still has to go through the MESSAGE IN
phase in order to get to BUS FREE phase. The main loop can do nothing
useful until BUS FREE, and sleeping just delays the phase transition.
2. If !cmd->device->disconnect and REQ is not already asserted when
NCR5380_information_transfer() is invoked, the function polls for REQ
for USLEEP_POLL jiffies. If REQ is not asserted, it then schedules
main() to execute after USLEEP_SLEEP jiffies and returns.
The idea is apparently to yeild the CPU while waiting for REQ.
This is conditional upon !cmd->device->disconnect, but there seems
to be no rhyme or reason for that. For example, the flag may be
unset because disconnection privilege was denied because the driver
has no IRQ. Or the flag may be unset because the device has never
needed to disconnect before. Or if the flag is set, disconnection
may have no relevance to the present bus phase.
Another deficiency of the existing algorithm is as follows. When the
driver has no IRQ, it prevents disconnection, and generally polls and
sleeps more than it would normally. Now, if the driver is going to poll
anyway, why not allow the target to disconnect? That way the driver can do
something useful with the bus instead of polling unproductively!
Avoid this pointless latency, complexity and guesswork by using
NCR5380_poll_politely() instead of scheduling main().
* For g_NCR5380, the time intervals for USLEEP_SLEEP and USLEEP_POLL are
200 ms and 10 ms, respectively. They are 20 ms and 200 ms respectively
for the other NCR5380 drivers. There doesn't seem to be any reason for
this discrepancy. The timing seems to have no relation to the type of
adapter. Bizarrely, the timing in g_NCR5380 seems to relate only to one
particular type of target device. This patch attempts to solve the
problem for all NCR5380 drivers and all target devices.
Signed-off-by: Finn Thain
---
drivers/scsi/NCR5380.c | 137
++-
drivers/scsi/NCR5380.h | 11 ---
drivers/scsi/atari_NCR5380.c | 24 ++-
drivers/scsi/g_NCR5380.c |4 -
4 files changed, 15 insertions(+), 161 deletions(-)
Reviewed-by: Hannes Reinecke
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
h...@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
