From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5A00617ADF7 for ; Tue, 6 Aug 2024 14:28:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722954511; cv=none; b=IgCK8lJEZDfRT6EyEDIIHsGvSm+AaTzRBOzJedEEpJu/yKEu+ejDL1AtYLWWLXldqL1I5WmBStbRQ3xzFskz4HxfbWAuP5TxxfgP5rfanJQlSzd3JOWxMZjWTbQ1URt8PQNA4jk98k17Ydq8GMuvsW9D+uY9urbx4WggwXYGW/g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722954511; c=relaxed/simple; bh=SaP5cRy/OYC03xi1zF6CDYg2u9FOuHqEgz8RDz62tMI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YAtpnPHoSRkEGrX+ifJ7oR2WNooaQh+T3IbWM2Nw0/jDd+QMInHWMmOD0hzOZ+hFb3HDZ8L5mkVVLWMq2YHwqQU9T5nmWlf77tD7+ubt+PyKFZr+YGGXKquFTo1rKRATKTnyru39hfEJYgEHXD3HHMGx+Xk2MZsfLhrO9GM39fw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=VhNCerMZ; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VhNCerMZ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722954509; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=WNQmn+tRRoRyrDQG+lSCrdnCGsmPfdPEgFqSTU9jbvg=; b=VhNCerMZZkt0qCjkczeeBwDeFv+Cg50Lh66L8nX4VTAFhu6ym9uH4h169T1VKN65CmtCAb VcmFOO1ZFuaZWZq47zs4GqhzIwzq3kHbNw2u9bDQyA9D4xamjnnFkR9Utja7UsbbQojimn qDNMY5wJnG75H3VERovCirb2ErRzgAY= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-684-i-G5OndxPNmiStgky985Uw-1; Tue, 06 Aug 2024 10:28:26 -0400 X-MC-Unique: i-G5OndxPNmiStgky985Uw-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CE8AF1914193; Tue, 6 Aug 2024 14:27:38 +0000 (UTC) Received: from fedora (unknown [10.72.116.14]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9C2BA1956046; Tue, 6 Aug 2024 14:26:56 +0000 (UTC) Date: Tue, 6 Aug 2024 22:26:50 +0800 From: Ming Lei To: Pavel Begunkov Cc: Jens Axboe , io-uring@vger.kernel.org, linux-block@vger.kernel.org, Kevin Wolf , ming.lei@redhat.com Subject: Re: [PATCH V4 4/8] io_uring: support SQE group Message-ID: References: <20240706031000.310430-1-ming.lei@redhat.com> <20240706031000.310430-5-ming.lei@redhat.com> <0fa0c9b9-cfb9-4710-85d0-2f6b4398603c@gmail.com> <5fd602d8-0c0b-418a-82bc-955ab0444b1e@gmail.com> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On Tue, Aug 06, 2024 at 04:38:08PM +0800, Ming Lei wrote: > On Mon, Jul 29, 2024 at 02:58:58PM +0100, Pavel Begunkov wrote: > > On 7/25/24 11:33, Ming Lei wrote: > > > On Wed, Jul 24, 2024 at 02:41:38PM +0100, Pavel Begunkov wrote: > > > > On 7/23/24 15:34, Ming Lei wrote: > > ... > > > > > But grp_refs is dropped after io-wq request reference drops to > > > > > zero, then both io-wq and nor-io-wq code path can be unified > > > > > wrt. dealing with grp_refs, meantime it needn't to be updated > > > > > in extra(io-wq) context. > > > > > > > > Let's try to describe how it can work. First, I'm only describing > > > > the dep mode for simplicity. And for the argument's sake we can say > > > > that all CQEs are posted via io_submit_flush_completions. > > > > > > > > io_req_complete_post() { > > > > if (flags & GROUP) { > > > > req->io_task_work.func = io_req_task_complete; > > > > io_req_task_work_add(req); > > > > return; > > > > } > > > > ... > > > > } > > > > > > OK. > > > > > > io_wq_free_work() still need to change to not deal with > > > next link & ignoring skip_cqe, because group handling( > > > > No, it doesn't need to know about all that. > > > > > cqe posting, link advance) is completely moved into > > > io_submit_flush_completions(). > > > > It has never been guaranteed that io_req_complete_post() > > will be the one completing the request, > > io_submit_flush_completions() can always happen. > > > > > > struct io_wq_work *io_wq_free_work(struct io_wq_work *work) > > { > > ... > > if (req_ref_put_and_test(req)) { > > nxt = io_req_find_next(req); > > io_free_req(); > > } > > } > > > > We queue linked requests only when all refs are dropped, and > > the group handling in my snippet is done before we drop the > > owner's reference. > > > > IOW, you won't hit io_free_req() in io_wq_free_work() for a > > leader unless all members in its group got completed and > > the leader already went through the code dropping those shared > > ublk buffers. > > If io_free_req() won't be called for leader, leader won't be added > to ->compl_reqs, and it has to be generated when all members are > completed in __io_submit_flush_completions(). > > For !io_wq, we can align to this way by not completing leader in > io_req_complete_defer(). > > The above implementation looks simpler, and more readable. Thinking of this issue further, looks the above is still not doable: 1) for avoiding to hit io_free_req(), extra req->refs has to be grabbed, then the leader's completion may not be notified. 2) 1) may be avoided by holding one leader's refcount for each member, and call req_ref_put_and_test(leader) when leader or member is completed, and post leader's CQE when leader's refs drops to zero. But there are other issues: - other req_ref_inc_not_zero() or req_ref_get() may cause leader's CQE post missed - the req_ref_put_and_test() in io_free_batch_list() can be called on group leader unexpectedly. both 1) and 2) need to touch io_req_complete_defer() for completing group leader Thanks, Ming