linux-kernel - Re: [patch] revert: [NET]: Fix races in net_rx

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Message-Id: <200707171607.08644.olaf.kirch@oracle.com>
Date:	Tue, 17 Jul 2007 16:07:07 +0200
From:	Olaf Kirch <olaf.kirch@...cle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jarek Poplawski <jarkao2@...pl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, davem@...emloft.net
Subject: Re: [patch] revert: [NET]: Fix races in net_rx_action vs netpoll

On Tuesday 17 July 2007 10:57, Ingo Molnar wrote:
> i've got a new observation: changing CONFIG_HZ from 250 to 1000 makes 
> the problem go away. So it's somehow also related to jiffies.

There are several "Tx Hang detected" messages in the log, which looks
a lot as if net_rx_action never runs, or at least never calls
dev->poll on the e1000 nic.

Can you check whether/how often it bails out of net_rx_action taking
the softnet_break path?

My suspicion right now is that dev->quota goes way negative when
pushing out netconsole output. Normally, we bump the quota in
__net_rx_schedule. But the whole point of the patch is that
netpoll has no business removing the device from the poll_list,
so it stays there, and we don't end up calling __net_rx_schedule
as often as we would otherwise.

Can you try what happens if you change netif_rx_complete to
something like this:

	if (test_bit(__LINK_STATE_POLL_LIST_FROZEN, &dev->state)) {
		dev->quota = dev->weight;
		return;
	}

This is just a hack to make sure that we don't go to insanely
negative quotas while sending packets through netpoll.

Olaf
-- 
Olaf Kirch  |  --- o --- Nous sommes du soleil we love when we play
okir@....de |    / | \   sol.dhoop.naytheet.ah kin.ir.samse.qurax
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