Messages in this thread | | | Date | Mon, 01 Oct 2007 00:12:59 -0700 (PDT) | Subject | Re: 2.6.21 -> 2.6.22 & 2.6.23-rc8 performance regression | From | David Miller <> |
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From: Eric Dumazet <dada1@cosmosbay.com> 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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