From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 053B3CA9EB9 for ; Thu, 24 Oct 2019 00:23:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C91302084B for ; Thu, 24 Oct 2019 00:23:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392821AbfJXAXJ convert rfc822-to-8bit (ORCPT ); Wed, 23 Oct 2019 20:23:09 -0400 Received: from smtpbgau1.qq.com ([54.206.16.166]:45098 "EHLO smtpbgau1.qq.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392153AbfJXAXJ (ORCPT ); Wed, 23 Oct 2019 20:23:09 -0400 X-QQ-mid: bizesmtp11t1571876579tlvkv2f1 Received: from [192.168.142.168] (unknown [218.76.23.26]) by esmtp6.qq.com (ESMTP) with id ; Thu, 24 Oct 2019 08:22:57 +0800 (CST) X-QQ-SSF: 00400000002000S0ZU90B00A0000000 X-QQ-FEAT: XDCR4pEWrpmfMgXPpcHQCpW0d63+G0DRr6mR+IYGwajyQrHNdLd3pQp7whop3 YEtTEfxb/PGNAPFJ/dOfmBMOvmbygm4tVX/ek2f6sKnHwPykVdZHdu45uc+6GnBfnLSxpLK X0hGlrH8VCqw1mLHal6LgV4wYggSAIHK8g15DmlMefu5Wm90yilFOmDLu0l9xzecmGxAa5N jj4fH7cCRGjTnWf8vLrMn0PMteq8ySPS1kEoU5WrCkwl8/NqnjEHx7FqbTYZkv2/rcjPbw/ IuJ6a13hdNCW/yLjFcrGoxFnb4i/KAuH4+DDp3YK5gK9lhzh4EVr6cqhjZl5Quo8Pc0jcz3 M4oGNHOgi/wOgb3pDE= X-QQ-GoodBg: 2 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.0 \(3594.4.19\)) Subject: Re: [PATCH] io_uring: ensure cq_entries is at least equal to or greater than sq_entries From: Jackie Liu In-Reply-To: Date: Thu, 24 Oct 2019 08:22:56 +0800 Cc: Jeff Moyer , linux-block@vger.kernel.org Content-Transfer-Encoding: 8BIT Message-Id: References: <1571795864-56669-1-git-send-email-liuyun01@kylinos.cn> To: Jens Axboe X-Mailer: Apple Mail (2.3594.4.19) X-QQ-SENDSIZE: 520 Feedback-ID: bizesmtp:kylinos.cn:qybgforeign:qybgforeign2 X-QQ-Bgrelay: 1 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org > 2019年10月24日 03:41，Jens Axboe 写道： > > On 10/23/19 12:42 PM, Jeff Moyer wrote: >> Jackie Liu writes: >> >>> If cq_entries is smaller than sq_entries, it will cause a lot of overflow >>> to appear. when customizing cq_entries, at least let him be no smaller than >>> sq_entries. >>> >>> Fixes: 95d8765bd9f2 ("io_uring: allow application controlled CQ ring size") >>> Signed-off-by: Jackie Liu >>> --- >>> fs/io_uring.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>> index b64cd2c..dfa9731 100644 >>> --- a/fs/io_uring.c >>> +++ b/fs/io_uring.c >>> @@ -3784,7 +3784,7 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p) >>> * to a power-of-two, if it isn't already. We do NOT impose >>> * any cq vs sq ring sizing. >>> */ >>> - if (!p->cq_entries || p->cq_entries > IORING_MAX_CQ_ENTRIES) >>> + if (p->cq_entries < p->sq_entries || p->cq_entries > IORING_MAX_CQ_ENTRIES) >> >> What if they're both zero? I think you want to keep that check. > > sq_entries being zero is already checked and failed at this point. > So I think the patch looks fine from that perspective. > > Is there really a strong reason to disallow this? Yes, it could > cause overflows, but it's just doing what was asked for. The > normal case is of course cq_entries being much larger than > sq_entries. > There are actually no other stronger reasons. I think it would be better to do a print job in liburing, but the kernel should still make a limit. Too many overflows will cause less efficiency. -- Jackie Liu