linux-kernel - Re: [PATCH] smp, ipi: Speed up IPI handling by invoking the callbacks in reverse order

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Message-ID: <20140604194731.GO13930@laptop.programming.kicks-ass.net>
Date:	Wed, 4 Jun 2014 21:47:31 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	akpm@...ux-foundation.org, fweisbec@...il.com, tglx@...utronix.de,
	hch@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] smp, ipi: Speed up IPI handling by invoking the
 callbacks in reverse order

On Thu, Jun 05, 2014 at 01:09:35AM +0530, Srivatsa S. Bhat wrote:
> The current implementation of lockless list (llist) has a drawback: if we
> want to traverse the list in FIFO order (oldest to newest), we need to
> reverse the list first (and this can be expensive if the list is large,
> since this is an O(n) operation).

Have you actually looked at the queue depth of this thing? Large queues
are a problem for interrupt latency.
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