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Message-ID: <4700ADB7.7050102@cosmosbay.com> Date: Mon, 01 Oct 2007 10:20:07 +0200 From: Eric Dumazet <dada1@...mosbay.com> To: Denys <nuclearcat@...learcat.com> Cc: David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org, netdev@...r.kernel.org Subject: Re: 2.6.21 -> 2.6.22 & 2.6.23-rc8 performance regression Denys a écrit : > Well, i can play a bit more on "live" servers. I have now hot-swap server with > full gentoo, where i can rebuild any kernel you want, with any applied patch. > But it looks more like not overhead, load becoming high too "spiky", and it is > not just permantenly higher. Also it is not normal that all system becoming > unresposive (for example ping 127.0.0.1 becoming 300ms for period, when usage > softirq jumps to 100%). > > Could you try a pristine 2.6.22.9 and some patch in secure_tcp_sequence_number() like : --- drivers/char/random.c.orig 2007-10-01 10:18:42.000000000 +0200 +++ drivers/char/random.c 2007-10-01 10:19:58.000000000 +0200 @@ -1554,7 +1554,7 @@ * That's funny, Linux has one built in! Use it! * (Networks are faster now - should this be increased?) */ - seq += ktime_get_real().tv64; + seq += ktime_get_real().tv64 / 1000; #if 0 printk("init_seq(%lx, %lx, %d, %d) = %d\n", saddr, daddr, sport, dport, seq); Thank you > On Mon, 01 Oct 2007 00:12:59 -0700 (PDT), David Miller wrote > >> 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. >> > > > -- > Denys Fedoryshchenko > Technical Manager > Virtual ISP S.A.L. > > > - 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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