linux-kernel - Re: all syscalls initially taking 4usec on a P4? Re: nonblocking UDPv4 recvfrom() taking 4usec @ 3GHz?

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: <20070220170232.GA4730@outpost.ds9a.nl>
Date:	Tue, 20 Feb 2007 18:02:32 +0100
From:	bert hubert <bert.hubert@...herlabs.nl>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	Andi Kleen <andi@...stfloor.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: all syscalls initially taking 4usec on a P4? Re: nonblocking UDPv4 recvfrom() taking 4usec @ 3GHz?

On Tue, Feb 20, 2007 at 07:41:25PM +0300, Evgeniy Polyakov wrote:

> It can be recvfrom only problem - syscall overhead on my p4 (core duo,
> debian testing) is bout 300 usec - to test I ran read('dev/zero', &data,
> 0) in a loop.

nsec I assume?

The usec numbers for read(fd, &c, 0) where fd is /dev/zero:
1.557667, 0.627667, 0.447333, 0.440000, 0.440000, 0.440000, 0.442333,
0.440000, 0.440000, 0.442333, 0.442333, 0.440000, 0.440000, 0.442333,
0.442667, 0.440000, 0.440000, 0.440000, 0.442333, 0.442667,

In usecs. Notice the same declining figure, but not as pronounced. With a
sleep(1) in between, we get:
1.692667, 1.800000, 0.782667, 1.282667, 0.665000, 0.980000, 0.925000,
0.887667, 0.662667, 0.862667, 1.077333, 1.442333, 0.660000, 1.890000,
0.672333, 0.795000, 0.647667, 0.692333, 0.750000, 0.865000,

This doesn't look all that unhealthy.

> Could you try to hack recvfrom() for your socket to always copy some
> empty buffer and check the results without waiting for packet?

That might be out of my reach before tomorrow :-)

> If you are not hurry I can test it myself tomorrow.

Thanks. My major problem is that in my measurements, I quite often see the
'worst case' 4usec result. It would not be a problem if it happens only
once, of course.

	Bert

-- 
http://www.PowerDNS.com      Open source, database driven DNS Software 
http://netherlabs.nl              Open and Closed source services
-
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/