On Wed, 2018-08-01 at 07:29 +0000, JABLONSKY Jan wrote: > The Watchdog workqueue in igb driver is scheduled every 2s for each > network interface. That includes updating a statistics protected by > spinlock. Function igb_update_stats in this case will be protected > against preemption. According to number of a statistics registers > (cca 60), processing this function might cause additional cpu load > on CPU0. > > In case of statistics spinlock may be replaced with mutex, which > reduce latency on CPU0. > > > # Measurements > Measurements were performed on Intel Atom E3950 (Quad-Core), > E3930 (Dual-Core) > > # Cyclictest > High latency is always on CPU0 which might be in range > from 70us to 140us (sometimes higher) > > > # cyclictest -l1000000 -Smp90 -i200 -q > > # E3930 > # default > T: 0 ( 1745) P:90 I:200 C:1000000 Min: 2 Act: 3 Avg: 3 Max: 72 > T: 1 ( 1746) P:90 I:700 C: 285737 Min: 3 Act: 4 Avg: 3 Max: 13 > > # with patch > T: 0 ( 932) P:90 I:200 C:1000000 Min: 2 Act: 3 Avg: 3 Max: 22 > T: 1 ( 933) P:90 I:700 C: 285736 Min: 2 Act: 3 Avg: 3 Max: 12 > > > # E3950 > # default > T: 0 ( 1103) P:90 I:200 C:1000000 Min: 2 Act: 2 Avg: 2 Max: 89 > T: 1 ( 1104) P:90 I:700 C: 285738 Min: 2 Act: 4 Avg: 2 Max: 9 > T: 2 ( 1105) P:90 I:1200 C: 166678 Min: 2 Act: 5 Avg: 3 Max: 22 > T: 3 ( 1106) P:90 I:1700 C: 117653 Min: 2 Act: 6 Avg: 2 Max: 13 > > # with patch > T: 0 ( 879) P:90 I:200 C:1000000 Min: 2 Act: 3 Avg: 3 Max: 26 > T: 1 ( 880) P:90 I:700 C: 285729 Min: 3 Act: 4 Avg: 3 Max: 22 > T: 2 ( 881) P:90 I:1200 C: 166672 Min: 3 Act: 7 Avg: 3 Max: 24 > T: 3 ( 882) P:90 I:1700 C: 117649 Min: 3 Act: 7 Avg: 3 Max: 8 > > > Additionally I think updating statistics and watchdog task should > be implemented in 2 separated ways > > Patch is created against a linux-4.4 > > Reviewed also by: Bernhard Kaindl <bernhard.kai...@thalesgroup.com> > > Signed-off-by: Jan Jablonsky <jan.jablon...@thalesgroup.com> > --- > drivers/net/ethernet/intel/igb/igb.h | 2 +- > drivers/net/ethernet/intel/igb/igb_ethtool.c | 4 ++-- > drivers/net/ethernet/intel/igb/igb_main.c | 14 +++++++------- > 3 files changed, 10 insertions(+), 10 deletions(-)
NACK, as is. This patch is malformed, as well as does not apply to the current net-next tree. Since the jist of this change is to wrap statistical updates with mutex lock versus spin locks, I will put together a patch agains the latest net-next tree for your review Jan.
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