From: Eric Dumazet <[email protected]>
Date: Mon, 01 Oct 2007 07:59:12 +0200
> No problem here on bigger servers, so I CC David Miller and netdev
> on this one. AFAIK do_gettimeofday() and ktime_get_real() should
> use the same underlying hardware functions on PC and no performance
> problem should happen here.
One thing that jumps out at me is that on 32-bit (and to a certain
extent on 64-bit) there is a lot of stack accesses and missed
optimizations because all of the work occurs, and gets expanded,
inside of ktime_get_real().
The timespec_to_ktime() inside of there constructs the ktime_t return
value on the stack, then returns that as an aggregate to the caller.
That cannot be without some cost.
ktime_get_real() is definitely a candidate for inlining especially in
these kinds of cases where we'll happily get computations in local
registers instead of all of this on-stack nonsense. And in several
cases (if the caller only needs the tv_sec value, for example)
computations can be elided entirely.
It would be constructive to experiment and see if this is in fact part
of the problem.
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