Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932276AbaFBOPw (ORCPT ); Mon, 2 Jun 2014 10:15:52 -0400 Received: from mail-pd0-f170.google.com ([209.85.192.170]:43395 "EHLO mail-pd0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932173AbaFBOPs (ORCPT ); Mon, 2 Jun 2014 10:15:48 -0400 Message-ID: <538C8712.20809@kernel.dk> Date: Mon, 02 Jun 2014 08:15:46 -0600 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Rusty Russell , Ming Lei CC: Linux Kernel Mailing List , "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org Subject: Re: [PATCH] block: virtio_blk: don't hold spin lock during world switch References: <1401418169-3361-1-git-send-email-ming.lei@canonical.com> <5387F8B2.1070509@kernel.dk> <5387FC96.4030508@kernel.dk> <877g537q6d.fsf@rustcorp.com.au> <53888D08.1050602@kernel.dk> <87sino5cl2.fsf@rustcorp.com.au> In-Reply-To: <87sino5cl2.fsf@rustcorp.com.au> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014-06-01 19:23, Rusty Russell wrote: > Jens Axboe writes: >> On 2014-05-30 00:10, Rusty Russell wrote: >>> Jens Axboe writes: >>>> If Rusty agrees, I'd like to add it for 3.16 with a stable marker. >>> >>> Really stable? It improves performance, which is nice. But every patch >>> which goes into the kernel fixes a bug, improves clarity, improves >>> performance or adds a feature. I've now seen all four cases get CC'd >>> into stable. >>> >>> Including some of mine explicitly not marked stable which get swept up >>> by enthusiastic stable maintainers :( >>> >>> Is now there *any* patch short of a major rewrite which shouldn't get >>> cc: stable? >> >> I agree that there's sometimes an unfortunate trend there. I didn't >> check, but my assumption was that this is a regression after the blk-mq >> conversion, in which case I do think it belongs in stable. > > No, it's always been that way. In the original driver the entire "issue > requests" function was under the lock. > > It was your mq conversion which made this optimization possible, and > also made it an optimization: now other the queues can continue while > this one is going. Ah, I stand corrected, you are right. I had this recollection that the prepare and kick where separate before as well, but apparently just bad memory. >> But in any case, I think the patch is obviously correct and the wins are >> sufficiently large to warrant a stable inclusion even if it isn't a >> regression. > > If you're running SMP under an emulator where exits are expensive, then > this wins. Under KVM it's marginal at best. > > Locking changes which are "obviously correct" make me nervous, too :) I tend to agree. But I think this one is simple enough to warrant doing it, when the performance increase is as large as it is. > But IIRC last KS the argument is that not *enough* is going into stable, > not that stable isn't stable enough. So maybe it's a non-problem? In principle, pushing the patch to stable definitely isn't an issue with the stable crew. And yes, they apparently do want more stuff. If you look at it from the distro side, having a stable(r) repository is a no brainer. And they'd want to pick this patch anyway, so... -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/