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Re: [announce] [patch] limiting IRQ load, irq-rewrite-2.4.11-B5

To: Ingo Molnar <mingo@xxxxxxx>
Subject: Re: [announce] [patch] limiting IRQ load, irq-rewrite-2.4.11-B5
From: jamal <hadi@xxxxxxxxxx>
Date: Wed, 3 Oct 2001 20:53:28 -0400 (EDT)
Cc: <linux-kernel@xxxxxxxxxxxxxxx>, Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>, Robert Olsson <Robert.Olsson@xxxxxxxxxxx>, Benjamin LaHaise <bcrl@xxxxxxxxxx>, <netdev@xxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxx>, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>, Simon Kirby <sim@xxxxxxxxxxxxx>
In-reply-to: <Pine.LNX.4.33.0110031749030.8633-100000@xxxxxxxxxxxxxxxxxxxxx>
Sender: owner-netdev@xxxxxxxxxxx

On Wed, 3 Oct 2001, Ingo Molnar wrote:

> On Wed, 3 Oct 2001, jamal wrote:
> > use the netif_rx() return code and hardware flowcontrol to fix it.
> i'm using hardware flowcontrol in the patch, but at a different, higher
> level. This part of the do_IRQ() code disables the offending IRQ source:
>       [...]
>         desc->status |= IRQ_MITIGATED|IRQ_PENDING;
>         __disable_irq(desc, irq);
> which in turn stops that device as well sooner or later. Optionally, in
> the future, this can be made more finegrained for chipsets that support
> device-independent IRQ mitigation features, like the USB 2.0 EHCI feature
> mentioned by David Brownell.

I think each subsytem should be in charge of its own fate. USB applies in
whatever subsystem it belongs to. Cooperating subsystems doing what os
best for the system.

> i'd prefer it if all subsystems and drivers in the kernel behaved properly
> and limited their IRQ load - but this does not always happen and users are
> hit by irq overload situations.

Your patch with Linus' idea of "flag mask" would be more acceptable as a
last resort. All subsytems should be cooperative and we resort to this to
send misbehaving kids to their room.

> Your NAPI patch, or any driver/subsystem that does flowcontrol accurately
> should never be affected by it in any way. No overhead, no performance
> hit.

so far your appraoch is that of a shotgun i.e  "let me fire in
that crowd and i'll hit my target but dont care if i take down a few
more"; regardless of how noble the reasoning is, it's  as Linus described
it -- a sledge hammer.


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