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Date: Fri, 21 May 2010 11:33:00 +1000 From: Nick Piggin <npiggin@...e.de> To: Manfred Spraul <manfred@...orfullife.com> Cc: linux-kernel@...r.kernel.org Subject: Re: [patch 2/3] ipc: use shifts to extract seq/idx On Thu, May 20, 2010 at 08:16:24PM +0200, Manfred Spraul wrote: > On 05/20/2010 09:00 AM, Nick Piggin wrote: > >All the ipc ids and sequences are signed integers, so power of 2 > >sequence multiplier does not work so well. Convert it to use shifts, > >which improves generated code particularly in ipc_lock/ipc_lock_check > >fast paths. > > > Have you checked the asm output? Yep, it's quite improved (although this isn't a particularly hot path I thought it is a good cleanup). > I would expect that gcc auto-optimizes constant divides by power-of-two. It can't with signed I guess. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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