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Date: Mon, 1 Oct 2007 15:10:15 +0300 From: "Denys" <nuclearcat@...learcat.com> To: Eric Dumazet <dada1@...mosbay.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 Not able to compile kernel with patch drivers/built-in.o: In function `secure_tcp_sequence_number': (.text+0x3ad02): undefined reference to `__divdi3' make: *** [.tmp_vmlinux1] Error 1 On Mon, 01 Oct 2007 10:20:07 +0200, Eric Dumazet wrote > Denys a : > > 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. > > > > > > -- Denys Fedoryshchenko Technical Manager Virtual ISP S.A.L. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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