From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933247AbaFJBfT (ORCPT ); Mon, 9 Jun 2014 21:35:19 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:18543 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932345AbaFJBfS (ORCPT ); Mon, 9 Jun 2014 21:35:18 -0400 Message-ID: <539660F9.9060408@oracle.com> Date: Tue, 10 Jun 2014 09:35:53 +0800 From: Junxiao Bi User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Jens Axboe , Andreas Mohr CC: linux-kernel@vger.kernel.org Subject: Re: [PATCH] block: make nr_requests tunable for loop References: <20140609072942.GA30728@rhlx01.hs-esslingen.de> <5395D88C.6070007@kernel.dk> In-Reply-To: <5395D88C.6070007@kernel.dk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Source-IP: ucsinet22.oracle.com [156.151.31.94] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/09/2014 11:53 PM, Jens Axboe wrote: > On 2014-06-09 01:29, Andreas Mohr wrote: >> Hi, >> >> having had a look at current mainline sources, >> frankly I've (well, initially...) got trouble understanding >> what this patch is doing. >> >> It's replacing an aggressive error-type bail-out (-EINVAL) for NULL >> request_fn >> with an inoccuous-looking "return ret;", yet that ret content currently >> *implicitly* is a >= 0 value (resulting from processing by earlier code >> which may or may not get incomprehensibly rewritten in future). >> I don't understand the reasons for this huge change in return value >> handling >> (since it's now not assigning a specific return value >> for this modified bail-out case). >> >> OK, well... you could say that since all this function ever was >> interested in is the result value of queue_var_store() >> (except for error bail-out cases), doing an interim "return ret;" >> (which is exactly what the function tail is also doing) >> is exactly right. >> >> But still simple textual appearance of the resulting patch hunks >> seems strangely asymmetric >> which may easily be a canary for structurally wrong layering of this >> function. >> Not to mention the now required extra spin_unlock_irq() >> in interim return handler... >> >> >> Well, after further analysis I would come to the conclusion >> that in general queue_requests_store() does a LOT more than it should - >> since blk-sysfs.c's only (expected!) purpose is >> to do parameterization of request_queue behaviour as gathered >> from sysfs attribute space, >> all that function should ever be concerned with is parsing that sysfs >> value >> and then calling a blk helper for configuration of that very >> attribute value >> which would *internally* do all the strange internal queue magic >> that is currently being updated *open-coded* >> at this supposedly *sysfs*-specific place. Ugh. >> Main question here: what would one do if one decided to rip out sysfs >> and use something entirely different for parameterization? >> Yeah indeed - thought so... >> >> >> So yeah, I'd definitely say that that function is lacking some cleanup >> which would possibly then even lead (or: would have led ;) >> to a much more nicely symmetric textual appearance >> of the patch hunk of the small but quite likely useful change >> that you currently intend to have here. > > If you are done ranting, look at the current tree where it has been > split out. There was no reason to have it split before, since the > sysfs entry point was the only place where we updated nr_requests. If > that code has been duplicated, there would have been a justified > reason for writing two pages about it. Yes, agree, this is the only place updating nr_requests, we can split it as a separated function if it needs updating at some other places in future.