From: Pekka Pietikainen <pp@ee.oulu.fi>
To: Jamie Lokier <jamie@shareable.org>
Cc: "David S. Miller" <davem@redhat.com>, Andi Kleen <ak@suse.de>,
linux-kernel@vger.kernel.org
Subject: Re: Fire Engine??
Date: Wed, 26 Nov 2003 23:54:55 +0200 [thread overview]
Message-ID: <20031126215455.GA15502@ee.oulu.fi> (raw)
In-Reply-To: <20031126200153.GG14383@mail.shareable.org>
On Wed, Nov 26, 2003 at 08:01:53PM +0000, Jamie Lokier wrote:
> > Andi, I know this is a problem, but for the millionth time your idea
> > does not work because we don't know if the user asked for the timestamp
> > until we are deep within the recvmsg() processing, which is long after
> > the packet has arrived.
>
> Do the timestamps need to be precise and accurately reflect the
> arrival time in the irq handler? Or, for TCP timestamps, would it be
> good enough to use the time when the protocol handlers are run, and
> only read the hardware clock once for a bunch of received packets? Or
> even use jiffies?
> Apart from TCP, precise timestamps are only used for packet capture,
> and it's easy to keep track globally of whether anyone has packet
> sockets open.
It should probably noted that really hardcore timestamp users
have their NICs do it for them, since interrupt coalescing
makes timestamps done in the kernel too inaccurate for them even
if rdtsc is used (http://www-didc.lbl.gov/papers/SCNM-PAM03.pdf)
Not that it's anywhere near a univeral solution since more or less only
one brand of NICs supports them.
It would probably be a useful experiment to see whether the performance is
improved in a noticeable way if say jiffies were used. If so, it might be a
reasonable choice for a configurable option, if not then not.
Isn't stuff like this the reason why the experimental network patches tree
that was announced a while back is out there? ;-)
next prev parent reply other threads:[~2003-11-26 21:55 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <BAY1-DAV15JU71pROHD000040e2@hotmail.com.suse.lists.linux.kernel>
[not found] ` <20031125183035.1c17185a.davem@redhat.com.suse.lists.linux.kernel>
2003-11-26 9:53 ` Fire Engine?? Andi Kleen
2003-11-26 11:35 ` John Bradford
2003-11-26 18:50 ` Mike Fedyk
2003-11-26 19:19 ` Diego Calleja García
2003-11-26 19:59 ` Mike Fedyk
2003-11-27 3:54 ` Bill Huey
2003-11-26 15:00 ` Trond Myklebust
2003-11-26 23:01 ` Andi Kleen
2003-11-26 23:23 ` Trond Myklebust
2003-11-26 23:38 ` Andi Kleen
2003-11-26 19:30 ` David S. Miller
2003-11-26 19:58 ` Paul Menage
2003-11-26 20:03 ` David S. Miller
2003-11-26 22:29 ` Andi Kleen
2003-11-26 22:36 ` David S. Miller
2003-11-26 22:56 ` Andi Kleen
2003-11-26 23:13 ` David S. Miller
2003-11-26 23:29 ` Andi Kleen
2003-11-26 23:41 ` Ben Greear
2003-11-27 0:01 ` Fast timestamps David S. Miller
2003-11-27 0:30 ` Mitchell Blank Jr
2003-11-27 1:57 ` Ben Greear
2003-11-26 20:01 ` Fire Engine?? Jamie Lokier
2003-11-26 20:04 ` David S. Miller
2003-11-26 21:54 ` Pekka Pietikainen [this message]
2003-11-26 20:22 ` Theodore Ts'o
2003-11-26 21:02 ` David S. Miller
2003-11-26 21:24 ` Jamie Lokier
2003-11-26 21:38 ` David S. Miller
2003-11-26 23:43 ` Jamie Lokier
2003-11-26 21:34 ` Arjan van de Ven
2003-11-26 22:58 ` Andi Kleen
2003-11-27 12:16 ` Ingo Oeser
2003-11-26 22:39 ` Andi Kleen
2003-11-26 22:46 ` David S. Miller
2003-11-26 0:15 Mr. BOFH
2003-11-26 2:30 ` David S. Miller
2003-11-26 5:41 ` Valdis.Kletnieks
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