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Ivan Vecera ea558de723 i40e: Enforce software interrupt during busy-poll exit 
As for ice bug fixed by commit b7306b42be ("ice: manage interrupts
during poll exit") followed by commit 23be7075b3 ("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: 0bcd952fee ("ethernet/intel: consolidate NAPI and NAPI exit")
Reported-by: Hugo Ferreira <hferreir@redhat.com>
Reviewed-by: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
History 2024-03-26 08:34:40 -07:00
arch bpf-for-netdev 2024-03-26 12:55:18 +01:00
block vfs-6.9-rc1.fixes 2024-03-18 09:15:50 -07:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto This update includes the following changes: 2024-03-15 14:46:54 -07:00
Documentation Including fixes from CAN, netfilter, wireguard and IPsec. 2024-03-21 14:50:39 -07:00
drivers i40e: Enforce software interrupt during busy-poll exit 2024-03-26 08:34:40 -07:00
fs Driver core changes for 6.9-rc1 2024-03-21 13:34:15 -07:00
include bpf-for-netdev 2024-03-26 12:55:18 +01:00
init Kbuild updates for v6.9 2024-03-21 14:41:00 -07:00
io_uring for-6.9/io_uring-20240310 2024-03-11 11:35:31 -07:00
ipc sysctl changes for v6.9-rc1 2024-03-18 14:59:13 -07:00
kernel bpf-for-netdev 2024-03-26 12:55:18 +01:00
lib Kbuild updates for v6.9 2024-03-21 14:41:00 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm Kbuild updates for v6.9 2024-03-21 14:41:00 -07:00
net tcp: properly terminate timers for kernel sockets 2024-03-25 19:51:57 -07:00
rust Kbuild updates for v6.9 2024-03-21 14:41:00 -07:00
samples Tracing updates for 6.9: 2024-03-18 15:11:44 -07:00
scripts bpf-for-netdev 2024-03-26 12:55:18 +01:00
security - Kuan-Wei Chiu has developed the well-named series "lib min_heap: Min 2024-03-14 18:03:09 -07:00
sound TTY/Serial driver update for 6.9-rc1 2024-03-21 12:44:10 -07:00
tools bpf-for-netdev 2024-03-26 12:55:18 +01:00
usr Kbuild updates for v6.8 2024-01-18 17:57:07 -08:00
virt KVM Xen and pfncache changes for 6.9: 2024-03-11 10:42:55 -04:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: create a list of all built DTB files 2024-02-19 18:20:39 +09:00
.mailmap bpf-for-netdev 2024-03-26 12:55:18 +01:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Not a ton of stuff happening in the clk framework in this pull request. We got 2024-03-15 11:48:01 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS bpf-for-netdev 2024-03-26 12:55:18 +01:00
Makefile Kbuild updates for v6.9 2024-03-21 14:41:00 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.