From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f54.google.com (mail-wr1-f54.google.com [209.85.221.54]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5DE981AAE05; Tue, 10 Sep 2024 20:31:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.54 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726000283; cv=none; b=Rd+8zT78j8QTBmmTK54RJKyFArLiTWeT3alVPNO49+orjGhT8AUlvCyaPHycb+RyD8BdxWjCANAhUVPUtFf97t1NwP5iIb647NddHdXrK3fgxDyTdM3KDX/uxVNZQAFdaj0Hef48R3tdjpwi+9A4nhoj8d10GsIxi5fjpOHTCtA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726000283; c=relaxed/simple; bh=d8gRAj5vL5jfkxzb01sVp5sumJst8wcVt3uxd4mgmVs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MDtQ+xbt8t/ehNYT/bqbehj9sgrjdA/1D86X5+mJZgySgcV1XRTcRbjA9sFKj3C1kzIqTcoZaa+eFj5dJQtQM7PF7f8llX0WdENoGHSztPDDFUNvDIaYm9JtlO3w3D2Gr+FyAmLTZvgcCJA80diXib4MMIYw5bk07Rf45rldFOs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=dejyExLh; arc=none smtp.client-ip=209.85.221.54 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="dejyExLh" Received: by mail-wr1-f54.google.com with SMTP id ffacd0b85a97d-374c1e5fe79so3944892f8f.1; Tue, 10 Sep 2024 13:31:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1726000280; x=1726605080; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=XGCuJMaxTlBSqr8ys2Ha2BHyFw84iEPU3729o1sKO7A=; b=dejyExLhqe3nx5xYIVeeYZ3/fi8CEIopV48ef2F3Ca3C1ZmJCH+FJEEJgaRRdjXrl0 kHQfbG0IWd0s78ZGg7dqmFnSxRhyot+NUOb8JOplWbcG5NebgC9mwpGAv+RvgTY8MEHf Bum6cgiPKf8QcbzkU8kQo6SCa1xmfUxBvcWSLOvjsX6Qg8ckYrqLOwyEs4FhdczzN0/W n/E1iImnBodGMxODyJyrnneShl0gEDsnFVjg+y8ubq+o40BmXdNWf2Da4X8GwgHj7s8u OJSrMe/d+Jfpwae4XVIO9vNBhZG/pyW66HBJ2myCXUwAHNfizX+0QEdAbbJ6b/ilBIkM MbfA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1726000280; x=1726605080; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=XGCuJMaxTlBSqr8ys2Ha2BHyFw84iEPU3729o1sKO7A=; b=JJRlEXAEUMvHdHFdYr7WX/JkDVLEyOmRW98/8T4MM4fewggew1FUSPdSt1H3P7386T rHChnc7M4DYk/TRCr0T/5zIdAHm8AtQkAPYswzOWgE6LPS1ezjarI6ZbmKmHLoP7tJMV NyvybTD/x9auGr6aql0ye0plZRBHImOka1uVXbAAAgi4mPnW9ojNdEt/5zTPbnHX4Glm rO7toTPEMO9CxBTMbMgkqvZqbO+6uCVs1g/i7F9RKxfSI06gHC1L18Q+yZkaHrKXJI74 LmDF3dyX+EQn9M47jGCib+nbz2Aqac5N1zTGNC4FGYW9wgIrNm5GfU2EYG5+tY6N25Ve 9aAw== X-Forwarded-Encrypted: i=1; AJvYcCU5ApTCiu9hexnubOXLrft9KeUjD/JYiLG3c4DAtJIjIDCUAtv8PaMqpVtqhaHiMEyojIx9MvUxCBNW2BE=@vger.kernel.org, AJvYcCUIyVY8oGuJZYloS7pgS1EuUmTgKlnObhFNxZmIRDK4I5hjtKzrhvqxeXQ7Gu0OVzgjNt5vhBCikw==@vger.kernel.org X-Gm-Message-State: AOJu0Yy0mdLk4UbjVQ60huljjVu1msDp2f4OmX2lnfpx/mN892sb8igH FeqY3PIntHO3YBowd52We43pcd8m8lyZ8j8FK6lZSmM9triC9rQTYoy/6CMWEgQ= X-Google-Smtp-Source: AGHT+IGXM0t2NmLdWsfjPV7+ZKlP+NFfe3EaE0588DJklyTB8AQ6YSTGade2hGZUJf5mwKglRSXSAA== X-Received: by 2002:a05:6000:184e:b0:378:7e74:cc25 with SMTP id ffacd0b85a97d-3788967e4e6mr14662245f8f.39.1726000279330; Tue, 10 Sep 2024 13:31:19 -0700 (PDT) Received: from [192.168.42.24] ([185.69.144.178]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42caeb8181csm122431855e9.33.2024.09.10.13.31.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Sep 2024 13:31:18 -0700 (PDT) Message-ID: Date: Tue, 10 Sep 2024 21:31:45 +0100 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V5 4/8] io_uring: support SQE group To: Ming Lei Cc: Jens Axboe , io-uring@vger.kernel.org, linux-block@vger.kernel.org, Kevin Wolf References: <20240808162503.345913-1-ming.lei@redhat.com> <20240808162503.345913-5-ming.lei@redhat.com> <3c819871-7ca3-47ea-b752-c4a8a49f8304@gmail.com> <36ae357b-bebe-4276-a8db-d6dccf227b61@gmail.com> <7050796e-be88-4e01-abdb-976baba2f83b@gmail.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/10/24 16:04, Ming Lei wrote: > On Tue, Sep 10, 2024 at 02:12:53PM +0100, Pavel Begunkov wrote: >> On 9/7/24 10:36, Ming Lei wrote: >> ... >>>>> Wrt. ublk, group provides zero copy, and the ublk io(group) is generic >>>>> IO, sometime IO_LINK is really needed & helpful, such as in ublk-nbd, >>>>> send(tcp) requests need to be linked & zc. And we shouldn't limit IO_LINK >>>>> for generic io_uring IO. >>>>> >>>>>> from nuances as such, which would be quite hard to track, the semantics >>>>>> of IOSQE_CQE_SKIP_SUCCESS is unclear. >>>>> >>>>> IO group just follows every normal request. >>>> >>>> It tries to mimic but groups don't and essentially can't do it the >>>> same way, at least in some aspects. E.g. IOSQE_CQE_SKIP_SUCCESS >>>> usually means that all following will be silenced. What if a >>>> member is CQE_SKIP, should it stop the leader from posting a CQE? >>>> And whatever the answer is, it'll be different from the link's >>>> behaviour. >>> >>> Here it looks easier than link's: >>> >>> - only leader's IOSQE_CQE_SKIP_SUCCESS follows linked request's rule >>> - all members just respects the flag for its own, and not related with >>> leader's >>> >>>> >>>> Regardless, let's forbid IOSQE_CQE_SKIP_SUCCESS and linked timeouts >>>> for groups, that can be discussed afterwards. >>> >>> It should easy to forbid IOSQE_CQE_SKIP_SUCCESS which is per-sqe, will do >>> it in V6. >>> >>> I am not sure if it is easy to disallow IORING_OP_LINK_TIMEOUT, which >>> covers all linked sqes, and group leader could be just one of them. >>> Can you share any idea about the implementation to forbid LINK_TIMEOUT >>> for sqe group? >> >> diff --git a/io_uring/timeout.c b/io_uring/timeout.c >> index 671d6093bf36..83b5fd64b4e9 100644 >> --- a/io_uring/timeout.c >> +++ b/io_uring/timeout.c >> @@ -542,6 +542,9 @@ static int __io_timeout_prep(struct io_kiocb *req, >> data->mode = io_translate_timeout_mode(flags); >> hrtimer_init(&data->timer, io_timeout_get_clock(data), data->mode); >> + if (is_timeout_link && req->ctx->submit_state.group.head) >> + return -EINVAL; >> + >> if (is_timeout_link) { >> struct io_submit_link *link = &req->ctx->submit_state.link; >> >> This should do, they already look into the ctx's link list. Just move >> it into the "if (is_timeout_link)" block. > > OK. > >> >> >>>>> 1) fail in linked chain >>>>> - follows IO_LINK's behavior since io_fail_links() covers io group >>>>> >>>>> 2) otherwise >>>>> - just respect IOSQE_CQE_SKIP_SUCCESS >>>>> >>>>>> And also it doen't work with IORING_OP_LINK_TIMEOUT. >>>>> >>>>> REQ_F_LINK_TIMEOUT can work on whole group(or group leader) only, and I >>>>> will document it in V6. >>>> >>>> It would still be troublesome. When a linked timeout fires it searches >>>> for the request it's attached to and cancels it, however, group leaders >>>> that queued up their members are discoverable. But let's say you can find >>>> them in some way, then the only sensbile thing to do is cancel members, >>>> which should be doable by checking req->grp_leader, but might be easier >>>> to leave it to follow up patches. >>> >>> We have changed sqe group to start queuing members after leader is >>> completed. link timeout will cancel leader with all its members via >>> leader->grp_link, this behavior should respect IORING_OP_LINK_TIMEOUT >>> completely. >>> >>> Please see io_fail_links() and io_cancel_group_members(). >>> >>>> >>>> >>>>>>> + >>>>>>> + lead->grp_refs += 1; >>>>>>> + group->last->grp_link = req; >>>>>>> + group->last = req; >>>>>>> + >>>>>>> + if (req->flags & REQ_F_SQE_GROUP) >>>>>>> + return NULL; >>>>>>> + >>>>>>> + req->grp_link = NULL; >>>>>>> + req->flags |= REQ_F_SQE_GROUP; >>>>>>> + group->head = NULL; >>>>>>> + if (lead->flags & REQ_F_FAIL) { >>>>>>> + io_queue_sqe_fallback(lead); >>>>>> >>>>>> Let's say the group was in the middle of a link, it'll >>>>>> complete that group and continue with assembling / executing >>>>>> the link when it should've failed it and honoured the >>>>>> request order. >>>>> >>>>> OK, here we can simply remove the above two lines, and link submit >>>>> state can handle this failure in link chain. >>>> >>>> If you just delete then nobody would check for REQ_F_FAIL and >>>> fail the request. >>> >>> io_link_assembling() & io_link_sqe() checks for REQ_F_FAIL and call >>> io_queue_sqe_fallback() either if it is in link chain or >>> not. >> >> The case we're talking about is failing a group, which is >> also in the middle of a link. >> >> LINK_HEAD -> {GROUP_LEAD, GROUP_MEMBER} >> >> Let's say GROUP_MEMBER fails and sets REQ_F_FAIL to the lead, >> then in v5 does: >> >> if (lead->flags & REQ_F_FAIL) { >> io_queue_sqe_fallback(lead); >> return NULL; >> } >> >> In which case it posts cqes for GROUP_LEAD and GROUP_MEMBER, >> and then try to execute LINK_HEAD (without failing it), which >> is wrong. So first we need: >> >> if (state.linked_link.head) >> req_fail_link_node(state.linked_link.head); > > For group leader, link advancing is always done via io_queue_next(), in > which io_disarm_next() is called for failing the whole remained link > if the current request is marked as FAIL. > >> >> And then we can't just remove io_queue_sqe_fallback(), because >> when a group is not linked there would be no io_link_sqe() >> to fail it. You can do: > > If one request in group is marked as FAIL, io_link_assembling() > will return true, and io_link_sqe() will fail it. Hmm, you're right, even though it's not a great way of doing it, i.e. pushing a req into io_link_sqe() even when linking has never been requested, but that's fine. I can drop a quick patch on top if it bothers me. -- Pavel Begunkov