On Thu, Jul 03, 2025 at 04:22:21PM +0800, Jason Xing wrote: > On Thu, Jul 3, 2025 at 4:15 PM Paolo Abeni <pabeni@xxxxxxxxxx> wrote: > > > > On 6/27/25 1:01 PM, Jason Xing wrote: > > > From: Jason Xing <kernelxing@xxxxxxxxxxx> > > > > > > This patch provides a setsockopt method to let applications leverage to > > > adjust how many descs to be handled at most in one send syscall. It > > > mitigates the situation where the default value (32) that is too small > > > leads to higher frequency of triggering send syscall. > > > > > > Considering the prosperity/complexity the applications have, there is no > > > absolutely ideal suggestion fitting all cases. So keep 32 as its default > > > value like before. > > > > > > The patch does the following things: > > > - Add XDP_MAX_TX_BUDGET socket option. > > > - Convert TX_BATCH_SIZE to tx_budget_spent. > > > - Set tx_budget_spent to 32 by default in the initialization phase as a > > > per-socket granular control. 32 is also the min value for > > > tx_budget_spent. > > > - Set the range of tx_budget_spent as [32, xs->tx->nentries]. > > > > > > The idea behind this comes out of real workloads in production. We use a > > > user-level stack with xsk support to accelerate sending packets and > > > minimize triggering syscalls. When the packets are aggregated, it's not > > > hard to hit the upper bound (namely, 32). The moment user-space stack > > > fetches the -EAGAIN error number passed from sendto(), it will loop to try > > > again until all the expected descs from tx ring are sent out to the driver. > > > Enlarging the XDP_MAX_TX_BUDGET value contributes to less frequency of > > > sendto() and higher throughput/PPS. > > > > > > Here is what I did in production, along with some numbers as follows: > > > For one application I saw lately, I suggested using 128 as max_tx_budget > > > because I saw two limitations without changing any default configuration: > > > 1) XDP_MAX_TX_BUDGET, 2) socket sndbuf which is 212992 decided by > > > net.core.wmem_default. As to XDP_MAX_TX_BUDGET, the scenario behind > > > this was I counted how many descs are transmitted to the driver at one > > > time of sendto() based on [1] patch and then I calculated the > > > possibility of hitting the upper bound. Finally I chose 128 as a > > > suitable value because 1) it covers most of the cases, 2) a higher > > > number would not bring evident results. After twisting the parameters, > > > a stable improvement of around 4% for both PPS and throughput and less > > > resources consumption were found to be observed by strace -c -p xxx: > > > 1) %time was decreased by 7.8% > > > 2) error counter was decreased from 18367 to 572 > > > > > > [1]: https://lore.kernel.org/all/20250619093641.70700-1-kerneljasonxing@xxxxxxxxx/ > > > > > > Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx> > > > > LGTM, waiting a little more for an explicit an ack from XDP maintainers. > > Thanks. No problem. Hey! i did review. Jason sorry but I got confused that you need to sort out the performance results on your side, hence the silence. > > > > > Side note: it could be useful to extend the xdp selftest to trigger the > > new code path. > > Roger that, sir. I will do it after this gets merged, maybe later this > month, still studying for various tests in recent days :) IMHO nothing worth testing with this patch per-se, it's rather the matter of performance. I would like however to ask you for follow-up with patch against xdpsock that adds support for using this new setsockopt (once we accept this onto kernel). > > Thanks, > Jason
