linux-kernel - Re: questions on NAPI processing latency and dropped network packets

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Message-ID: <20080115161705.0724250d@astralstorm.puszkin.org>
Date:	Tue, 15 Jan 2008 16:17:05 +0100
From:	Radoslaw Szkodzinski (AstralStorm) <lkml@...ralstorm.puszkin.org>
To:	"Chris Friesen" <cfriesen@...tel.com>
Cc:	Jarek Poplawski <jarkao2@...il.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: questions on NAPI processing latency and dropped network
 packets

On Tue, 15 Jan 2008 08:47:07 -0600
"Chris Friesen" <cfriesen@...tel.com> wrote:

> Jarek Poplawski wrote:
> 
> > IMHO, checking this with a current stable, which probably you are going
> > to do some day, anyway, should be 100% acceptable: giving some input to
> > netdev, while still working for yourself.
> 
> While I would love to do this, it's not that simple.
> 
> Some of our hardware is not supported on mainline, so we need per-kernel 
> version patches to even bring up the blade.  The blades netboot via a 
> jumbo-frame network, so kernel extensions are needed to handle setting 
> the MTU before mounting the rootfs.

Why? Can't you use a small initramfs to set it up?

> The blade in question uses CKRM 
> which doesn't exist for newer kernels so the problem may simply be 
> hidden by scheduling differences.

Current spiritual successor is Ingo's realtime patchset I guess.

> The userspace application uses other 
> kernel features that are not in mainline (and likely some of them won't 
> ever be in mainline--I know because I've tried).

What would these be? Some proc or sysfs files that were removed or
renamed?
Maybe they can be worked around w/o changing the application at all, or
very minor changes.

Also, be sure to check if there are pauses with other CPU hogs.

> Basically, the number of changes required for our environment makes it 
> difficult to just boot up the latest kernel.

Yes, adding an initramfs is non-trivial (some busybox + shell
scripting), but not all that hard either.
And maintaining one is easier than patching the kernel.
(usually 0 maintenance, maybe minor fixes sometimes)

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