linux-kernel - Re: [patch v2] epoll use a single inode ...

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <200703061828.00253.dada1@cosmosbay.com>
Date:	Tue, 6 Mar 2007 18:28:00 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch v2] epoll use a single inode ...

On Tuesday 06 March 2007 18:19, Linus Torvalds wrote:
> On Tue, 6 Mar 2007, Eric Dumazet wrote:
> > Something like :
> >
> > [PATCH] : Use reciprocal divides in sprintf()
>
> Try this on Core 2, and I suspect that you'll find that the hardware is
> actually *faster* than doing the shift/test, function call and the
> two multiplies.
>

Where do you see a function call ?

     448:       44 89 d0                mov    %r10d,%eax
     44b:       44 89 ea                mov    %r13d,%edx
     44e:       48 0f af c1             imul   %rcx,%rax
     452:       48 c1 e8 20             shr    $0x20,%rax
     456:       0f af d0                imul   %eax,%edx
     459:       49 29 d2                sub    %rdx,%r10
     45c:       43 0f b6 14 16          movzbl (%r14,%r10,1),%edx
     461:       41 89 c2                mov    %eax,%r10d
     464:       41 88 13                mov    %dl,(%r11)
     467:       49 ff c3                inc    %r11
     46a:       85 c0                   test   %eax,%eax
     46c:       75 da                   jne    448 <number+0x138>



> > Using reciprocal divides permits to change each divide by two multiplies,
> > less expensive on current CPUS.
>
> Are you sure?

I am going to test this, but at least on Opterons, the reciprocal divide I 
added into mm/slab.c gave me a nice speedup.

I am going to bench some stupid loop :

for (i = 0 ; i < 1000*1000 ; i++) {
	pipe(fds); close(fds[0]); close(fds[1]);
}

-
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/