Re: [PATCH net v4] i40e: Enforce software interrupt during busy-poll exit

[Michal Schmidt]

On Sat, Mar 16, 2024 at 12:38 PM Ivan Vecera <ivecera@xxxxxxxxxx> wrote:
> As for ice bug fixed by commit b7306b42beaf ("ice: manage interrupts
> during poll exit") followed by commit 23be7075b318 ("ice: fix software
> generating extra interrupts") I'm seeing the similar issue also with
> i40e driver.
>
> In certain situation when busy-loop is enabled together with adaptive
> coalescing, the driver occasionally misses that there are outstanding
> descriptors to clean when exiting busy poll.
>
> Try to catch the remaining work by triggering a software interrupt
> when exiting busy poll. No extra interrupts will be generated when
> busy polling is not used.
>
> The issue was found when running sockperf ping-pong tcp test with
> adaptive coalescing and busy poll enabled (50 as value busy_pool
> and busy_read sysctl knobs) and results in huge latency spikes
> with more than 100000us.
>
> The fix is inspired from the ice driver and do the following:
> 1) During napi poll exit in case of busy-poll (napo_complete_done()
>    returns false) this is recorded to q_vector that we were in busy
>    loop.
> 2) Extends i40e_buildreg_itr() to be able to add an enforced software
>    interrupt into built value
> 2) In i40e_update_enable_itr() enforces a software interrupt trigger
>    if we are exiting busy poll to catch any pending clean-ups
> 3) Reuses unused 3rd ITR (interrupt throttle) index and set it to
>    20K interrupts per second to limit the number of these sw interrupts.
>
> Test results
> ============
> Prior:
> [root@dell-per640-07 net]# sockperf ping-pong -i 10.9.9.1 --tcp -m 1000 --mps=max -t 120
> sockperf: == version #3.10-no.git ==
> sockperf[CLIENT] send on:sockperf: using recvfrom() to block on socket(s)
>
> [ 0] IP = 10.9.9.1        PORT = 11111 # TCP
> sockperf: Warmup stage (sending a few dummy messages)...
> sockperf: Starting test...
> sockperf: Test end (interrupted by timer)
> sockperf: Test ended
> sockperf: [Total Run] RunTime=119.999 sec; Warm up time=400 msec; SentMessages=2438563; ReceivedMessages=2438562
> sockperf: ========= Printing statistics for Server No: 0
> sockperf: [Valid Duration] RunTime=119.549 sec; SentMessages=2429473; ReceivedMessages=2429473
> sockperf: ====> avg-latency=24.571 (std-dev=93.297, mean-ad=4.904, median-ad=1.510, siqr=1.063, cv=3.797, std-error=0.060, 99.0% ci=[24.417, 24.725])
> sockperf: # dropped messages = 0; # duplicated messages = 0; # out-of-order messages = 0
> sockperf: Summary: Latency is 24.571 usec
> sockperf: Total 2429473 observations; each percentile contains 24294.73 observations
> sockperf: ---> <MAX> observation = 103294.331
> sockperf: ---> percentile 99.999 =   45.633
> sockperf: ---> percentile 99.990 =   37.013
> sockperf: ---> percentile 99.900 =   35.910
> sockperf: ---> percentile 99.000 =   33.390
> sockperf: ---> percentile 90.000 =   28.626
> sockperf: ---> percentile 75.000 =   27.741
> sockperf: ---> percentile 50.000 =   26.743
> sockperf: ---> percentile 25.000 =   25.614
> sockperf: ---> <MIN> observation =   12.220
>
> After:
> [root@dell-per640-07 net]# sockperf ping-pong -i 10.9.9.1 --tcp -m 1000 --mps=max -t 120
> sockperf: == version #3.10-no.git ==
> sockperf[CLIENT] send on:sockperf: using recvfrom() to block on socket(s)
>
> [ 0] IP = 10.9.9.1        PORT = 11111 # TCP
> sockperf: Warmup stage (sending a few dummy messages)...
> sockperf: Starting test...
> sockperf: Test end (interrupted by timer)
> sockperf: Test ended
> sockperf: [Total Run] RunTime=119.999 sec; Warm up time=400 msec; SentMessages=2400055; ReceivedMessages=2400054
> sockperf: ========= Printing statistics for Server No: 0
> sockperf: [Valid Duration] RunTime=119.549 sec; SentMessages=2391186; ReceivedMessages=2391186
> sockperf: ====> avg-latency=24.965 (std-dev=5.934, mean-ad=4.642, median-ad=1.485, siqr=1.067, cv=0.238, std-error=0.004, 99.0% ci=[24.955, 24.975])
> sockperf: # dropped messages = 0; # duplicated messages = 0; # out-of-order messages = 0
> sockperf: Summary: Latency is 24.965 usec
> sockperf: Total 2391186 observations; each percentile contains 23911.86 observations
> sockperf: ---> <MAX> observation =  195.841
> sockperf: ---> percentile 99.999 =   45.026
> sockperf: ---> percentile 99.990 =   39.009
> sockperf: ---> percentile 99.900 =   35.922
> sockperf: ---> percentile 99.000 =   33.482
> sockperf: ---> percentile 90.000 =   28.902
> sockperf: ---> percentile 75.000 =   27.821
> sockperf: ---> percentile 50.000 =   26.860
> sockperf: ---> percentile 25.000 =   25.685
> sockperf: ---> <MIN> observation =   12.277
>
> Fixes: 0bcd952feec7 ("ethernet/intel: consolidate NAPI and NAPI exit")
> Reported-by: Hugo Ferreira <hferreir@xxxxxxxxxx>
> Reviewed-by: Michal Schmidt <mschmidt@xxxxxxxxxx>

Yes, I am OK with v4.
Michal

> Signed-off-by: Ivan Vecera <ivecera@xxxxxxxxxx>