On Tuesday 12 December 2017 04:33 PM, Ananyev, Konstantin wrote:
-----Original Message-----
From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Matan Azrad
Sent: Tuesday, December 12, 2017 10:46 AM
To: Nikhil Agarwal <nikhil.agar...@linaro.org>; dev@dpdk.org
Cc: Hunt, David <david.h...@intel.com>; nikhil.agar...@nxp.com;
hemant.agra...@nxp.com; Yigit, Ferruh <ferruh.yi...@intel.com>
Subject: Re: [dpdk-dev] [PATCH 1/3] ethdev: add max burst size to device info
Hi Nikhil
-----Original Message-----
From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Nikhil Agarwal
Sent: Tuesday, December 12, 2017 12:05 PM
To: dev@dpdk.org
Cc: david.h...@intel.com; nikhil.agar...@nxp.com;
hemant.agra...@nxp.com; ferruh.yi...@intel.com
Subject: [dpdk-dev] [PATCH 1/3] ethdev: add max burst size to device info
Currently, if the rte_eth_rx_burst() function returns a value less than
*nb_pkts*, the application will assume that no more packets are present..
Some of the hw queue based hardware can only support smaller burst for RX
and TX and thus break the expectation of the rx_burst API.
Doesn't such like devices PMDs should try to retrieve multiple HW burst to
adjust the asked received packet number?
Same thought here...
Can't that limitation be hidden inside PMD by calling HW burst multiple times?
This might be required in some cases for performance.
It is possible that for each request containing N buffers, if the PMD
fetches all N (more than its preferred burst_size), cache misses reduce
the performance - especially for SoC with limited cache size.
Also, a complete cycle of
application->driver->hardware->driver->application can help driver
prefetch buffers - which, in case of hw burst looping, might be too
little to complete the prefetch cycle.
To summarize, indeed this is for performance specific cases and the idea
that @Matan gave for renaming 'perf_buf_size' to highlight this, sounds
logical.
Also if I am not mistaken - it would increase size of struct rte_eth_dev_info,
right?
If so, then it means ABI breakage.
Yes, deprecation notice should have been sent - if we continue with the
dev_info change. To me that looks as one of the option. Maybe, someone
on the list has a better idea.
Konstantin
This patch adds support to provide the maximum burst size that can be
supported by a given PMD. The dev_info is being memset to '0' in
rte_ethdev library. The value of '0' indicates that any value for burst size can
be supported i.e. no change for existing PMDs.
The application can now use the lowest available max_burst_size value for
rte_eth_rx_burst.
If you are talking about performance, maybe the right field to expose is something like
"perf_burst_size" or "preferred_burst_size".
I also suggest to expose different fields for RX and for TX.
Maybe the rte_eth_rx\tx_burst() descriptions should be updated.
Thanks
Matan.
Signed-off-by: Nikhil Agarwal <nikhil.agar...@linaro.org>
---
lib/librte_ether/rte_ethdev.h | 1 +
1 file changed, 1 insertion(+)
diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
index 341c2d6..3ab6f02 100644
--- a/lib/librte_ether/rte_ethdev.h
+++ b/lib/librte_ether/rte_ethdev.h
@@ -1047,6 +1047,7 @@ struct rte_eth_dev_info {
/** Configured number of rx/tx queues */
uint16_t nb_rx_queues; /**< Number of RX queues. */
uint16_t nb_tx_queues; /**< Number of TX queues. */
+ uint16_t max_burst_size; /**< MAX burst size, 0 for no limit. */
};
/**
--
2.7.4
