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Re: packet re-ordering on SMP machines.

To: Andi Kleen <ak@xxxxxxx>
Subject: Re: packet re-ordering on SMP machines.
From: jamal <hadi@xxxxxxxxxx>
Date: Tue, 27 Aug 2002 08:05:04 -0400 (EDT)
Cc: "Xiaoliang (David) Wei" <weixl@xxxxxxxxxxx>, Ben Greear <greearb@xxxxxxxxxxxxxxx>, Cheng Jin <chengjin@xxxxxxxxxxxxxx>, Cheng Hu <chenghu@xxxxxxxxxxxxxx>, Steven Low <slow@xxxxxxxxxxxxxx>, <netdev@xxxxxxxxxxx>
In-reply-to: <20020827131227.A16565@wotan.suse.de>
Sender: netdev-bounce@xxxxxxxxxxx



On Tue, 27 Aug 2002, Andi Kleen wrote:

>
> That is because of the lock it takes. Locks are always slow.

xtime_lock?

>
> Older kernels used gettimeoffset which ran without lock, but that was
> changed because in some very obscure cases it could cause non monotonous
> timestamps when the user turns on timestamp receiving to user space
> (kernel protocols do not care)
>
> Possibilities:
>
> - Ignore the problem and switch back to gettimeoffset again

Is it safe to call gettimeoffset without the lock?

> - Switch to gettimeoffset but add some correction step for the unlikely
> case that someone wants the timestamp from user space
> (would be my prefered solution)
> - Implement lockless gettimeofday like x86-64 or sparc
> (good one too, but likely slower than last)


ia64 seems to also have the lock.

cheers,
jamal


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