Vladislav Bolkhovitin wrote:
Cameron Harr wrote:
Bart Van Assche wrote:
On Mon, Oct 6, 2008 at 5:31 PM, Cameron Harr <[EMAIL PROTECTED]> wrote:
Thanks for the suggestion. As I look via vmstat, my CSw/s rate is
fairly
constant around 280K when scst_threads=1 (per Vu's suggestion) and
pops up
to ~330-340K CSw/s when scst_threads is set to 8.
Which threads are causing all those context switches ? You can find
this out by making sure that CONFIG_SCHEDSTATS=y is enabled in the
kernel .config and by running the following bash command:
( cd /proc && for p in [1-9]* ; do echo "$(<${p}/cmdline)
$(<${p}/schedstat)" ; done ) | sort -rn -k 3 | head
Thanks for the bash lesson :). It wasn't working how I think you had
planned because many processes have nothing in the cmdline file. So,
I touched up the command a bit, putting in the pid and displaying the
cmdline at the end so as not to mess up the sort:
( cd /proc && for p in [1-9]* ; do echo -e "$p:\t $(<${p}/schedstat)
\t\t$(<${p}/cmdline)" ; done ) | sort -rn -k 3 | head
Using that, and watching who's moving up in amount of time waiting,
the main culprits are all of the scst_threads when scst_threads=8,
and when threads=2, the culprit is srpt_thread.
After some code examination, I figured out that Vu has chosen a
"defensive programming" way ;): always switch to another thread.
I personally don't see why srpt_thread is needed at all. Vu, if you
think that the processing is too heavy weighted, you should rather use
tasklets instead.
SCST functions scst_cmd_init_done() and scst_rx_data() should be
called with context SCST_CONTEXT_DIRECT_ATOMIC from interrupt context
or SCST_CONTEXT_DIRECT from thread context. Then amount of context
switches per cmd will go to the same reasonable level <=1 as for
qla2x00t. \
You are correct - by default srp run in thread mode - srp can also run
in tasklet mode (parameter thread=0); however, the main trade of is
instability (in heavy tpc-h workload)
I already let Cameron know about this. We should have some prelim.
number from him soon (running with thread=0) and we need some quality
time to debug/fix the instability of some special workload
-Cameron
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