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Message-Id: <20071001.001259.28812610.davem@davemloft.net> Date: Mon, 01 Oct 2007 00:12:59 -0700 (PDT) From: David Miller <davem@...emloft.net> To: dada1@...mosbay.com Cc: nuclearcat@...learcat.com, linux-kernel@...r.kernel.org, netdev@...r.kernel.org Subject: Re: 2.6.21 -> 2.6.22 & 2.6.23-rc8 performance regression From: Eric Dumazet <dada1@...mosbay.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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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