Re: [PATCH] audit: Reduce overhead using a coarse clock

From: Mel Gorman
Date: Tue Jul 04 2017 - 12:53:15 EST

On Tue, Jul 04, 2017 at 09:23:55AM -0700, Deepa Dinamani wrote:
> > The patch in question has no explanation as to why a fully-accurate timestamp
> > is required and is likely an oversight. Using a coarser, but monotically
> > increasing, timestamp the overhead can be eliminated.
> You are right. I was trying to use ktime_get* functions preferably.
> I was aware that current_kernel_time64() could also be used if lesser
> granularity was preferred and that it was faster.
> I forgot to note that in the commit text.

Given the severe overhead (roughly 10% to redis, sysbench-threads), would
you be willing to accept the coarser granularity to avoid audit taking
a major performance hit? I didn't mention it in my own changelog but a
similar 10% hit is also visible in the will-it-scale microbenchmarks that
focus on system calls so it's a fairly broad impact.

Mel Gorman