From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: [PATCH] libata-sff: fix 32-bit PIO regression Date: Sun, 08 Feb 2009 19:19:07 -0500 Message-ID: <498F767B.9060701@pobox.com> References: <200902082253.07438.sshtylyov@ru.mvista.com> <498F5A25.90707@ru.mvista.com> <18831.28471.454273.451912@harpo.it.uu.se> <498F72C8.8020204@ru.mvista.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:33294 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752153AbZBIATd (ORCPT ); Sun, 8 Feb 2009 19:19:33 -0500 In-Reply-To: <498F72C8.8020204@ru.mvista.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Sergei Shtylyov Cc: Mikael Pettersson , Hugh Dickins , linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, alan@lxorguk.ukuu.org.uk, rjw@sisk.pl Sergei Shtylyov wrote: > Do you really think that the transfers having lengths non-divisible by > 4 make any *significant* percentage even on the ATAPI devices? I think > it's you who is really wrong. The answer depends on workload. Though rare, workloads do exist that involve a lot of oddball querying via weird, vendor-specific SCSI[-ish] commands. Moreover, the likelihood and cost of a branch mispredict are both low in this case, IMO. Or a more human version of the rule: if you have to have a long email thread about unlikely() placement, it is best just to avoid using unlikely() in that case at all. Branch prediction units in modern CPUs are damned good anyways, and there is always the likelihood that a human-placed unlikely() becomes wrong in the future. Plus the code is more readable without unlikely(), IMO. Jeff