linux-kernel - Re: [PATCH] i386-pda UP optimization

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]

Date:	Tue, 21 Nov 2006 15:12:57 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Andi Kleen <ak@...e.de>, Ingo Molnar <mingo@...e.hu>,
	akpm@...l.org, Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i386-pda UP optimization

Eric Dumazet wrote:
> for umask/getppid(), its a basic loop with 100.000.000 iterations

Ah, OK, so there's about 2.5-3.5ns difference due to the instructions
you removed.  That's very much in line with that I saw in my measurements.

> for read/write(), loop with 10.000.000 iterations

2 syscalls/iteration?  It's interesting you measured about the same
absolute time difference (.42s) even though you're doing 1/5th the
number of syscalls.

> elapsed time (/usr/bin/time ./prog)
> 10 runs, and the minimum time is taken.

Hm, but "time" measures user, system and real time.  You used real time?

> Hum... Do you mean a cache miss every time we do a syscall ? What
> could invalidate this cache exactly ?

Well, there might be a miss simply because the line got evicted.  But as
Andi pointed out, a hot benchmark like this is very unlikely to get any
cache misses unless there's something very unfortunate happening.

    J
-
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/