> On 6 Sep 2017, at 17:58, Santosh Shilimkar <santosh.shilim...@oracle.com> > wrote: > > On 9/6/2017 8:29 AM, Håkon Bugge wrote: >> In rds_send_xmit() there is logic to batch the sends. However, if >> another thread has acquired the lock, it is considered a race and we >> yield. The code incrementing the s_send_lock_queue_raced statistics >> counter did not count this event correctly. >> This commit removes a small race in determining the race and >> increments the statistics counter correctly. >> Signed-off-by: Håkon Bugge <haakon.bu...@oracle.com> >> Reviewed-by: Knut Omang <knut.om...@oracle.com> >> --- >> net/rds/send.c | 16 +++++++++++++--- >> 1 file changed, 13 insertions(+), 3 deletions(-) > Those counters are not really to give that accurate so > am not very keen to add additional cycles in send paths > and add additional code. Have you seen any real issue > or this is just a observation. s_send_lock_queue_raced > counter is never used to check for smaller increments > and hence the question.
Hi Santosh, Yes, I agree with accuracy of s_send_lock_queue_raced. But the main point is that the existing code counts some partial share of when it is _not_ raced. So, in the critical path, my patch adds one test_bit(), which hits the local CPU cache, if not raced. If raced, some other thread is in control, so I would not think the added cycles would make any big difference. I can send a v2 where the race tightening is removed if you like. Thxs, Håkon
