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=-8.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_MUTT 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 2BE35C04EB8 for ; Tue, 11 Dec 2018 03:22:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CE8A920645 for ; Tue, 11 Dec 2018 03:22:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1544498525; bh=FO9I1OCXE44/F8PRjLU1uMnj5r987K3vv0glqJU8rkE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=AjshcaEbC+xJh1FWi5WT9quuSz4sxr1x+JuRMl4Gs92WA5gXA3a/YgJJXsJqvAZbP kmPiPpVUO/OTJvqtGjjXtpsbbP9OloDusutQ2hceOByV51RDhrzjsl6R1r3zDzK2p/ 62tYS1HpN8+nCWsDS4L7uzltinyNF19o9VkowQGc= DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CE8A920645 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-block-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728627AbeLKDWE (ORCPT ); Mon, 10 Dec 2018 22:22:04 -0500 Received: from mail-yb1-f193.google.com ([209.85.219.193]:33366 "EHLO mail-yb1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728584AbeLKDWE (ORCPT ); Mon, 10 Dec 2018 22:22:04 -0500 Received: by mail-yb1-f193.google.com with SMTP id f125so6159495ybc.0; Mon, 10 Dec 2018 19:22:03 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=WZNmerNVp1OzoQvVK2tSTUhw2j6CZgTEH86VJHmZyEY=; b=GKb2SP422Og9aXteBCggxYkcj/IhViZy8dTo6WfDrdcJZuENf2BAutcLxILDRJ2CKC HdEq7OJiD1oiw+VyncHxes2CNycZAjg8F5mfCUQoOoUmthawil3J5YVGY1LdIPsOy0L0 eJ7lVraTiugN1I0m/EFH01ITmGLA486FiYt1L3ocvBjmqzj8LdZxzoaD9AcbB1KOyr+p DDWl2oY3c4PTrv//vAYRutu02BgCIRkE6HSl66UrX6TJa6XZrW64Enn/SA9cytT7JU0w vZV8hRrVRvLHYLLwJJEByl9s2TRCPmj2y7h1YuIUKrCTG3lBwg/pJxZjNmR4h0hTcES6 G5Hw== X-Gm-Message-State: AA+aEWY14qHpjQkZP+zHkyjJtRyI2G11GGNlg9NfCQqT8tUJmeiDEqq0 eg+UoqEgqKxNY+VZve4M/Kk= X-Google-Smtp-Source: AFSGD/Wcc9LMd74JAttNgCgQsp5UIy2Bi7zB07z4H9czoXyP1DinwFtIs89fAfs1i5xdldpX0AHRoQ== X-Received: by 2002:a25:1585:: with SMTP id 127-v6mr14699787ybv.208.1544498522650; Mon, 10 Dec 2018 19:22:02 -0800 (PST) Received: from dennisz-mbp.dhcp.thefacebook.com ([2620:10d:c091:180::1:c7f8]) by smtp.gmail.com with ESMTPSA id j6sm4403463ywi.110.2018.12.10.19.22.00 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Dec 2018 19:22:01 -0800 (PST) Date: Mon, 10 Dec 2018 22:21:59 -0500 From: Dennis Zhou To: Josef Bacik Cc: Jens Axboe , Tejun Heo , Johannes Weiner , kernel-team@fb.com, linux-block@vger.kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] block: fix iolat timestamp and restore accounting semantics Message-ID: <20181211032159.GB40583@dennisz-mbp.dhcp.thefacebook.com> References: <20181210163510.58985-1-dennis@kernel.org> <20181210182507.qtoj5egbflr5s366@macbook-pro-91.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181210182507.qtoj5egbflr5s366@macbook-pro-91.dhcp.thefacebook.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi Josef, On Mon, Dec 10, 2018 at 01:25:08PM -0500, Josef Bacik wrote: > On Mon, Dec 10, 2018 at 11:35:10AM -0500, Dennis Zhou wrote: > > The blk-iolatency controller measures the time from rq_qos_throttle() to > > rq_qos_done_bio() and attributes this time to the first bio that needs > > to create the request. This means if a bio is plug-mergeable or > > bio-mergeable, it gets to bypass the blk-iolatency controller. > > > > The recent series, to tag all bios w/ blkgs in [1] changed the timing > > incorrectly as well. First, the iolatency controller was tagging bios > > and using that information if it should process it in rq_qos_done_bio(). > > However, now that all bios are tagged, this caused the atomic_t for the > > struct rq_wait inflight count to underflow resulting in a stall. Second, > > now the timing was using the duration a bio from generic_make_request() > > rather than the timing mentioned above. > > > > This patch fixes the errors by accounting time separately in a bio > > adding the field bi_start. If this field is set, the bio should be > > processed by blk-iolatency in rq_qos_done_bio(). > > > > [1] https://lore.kernel.org/lkml/20181205171039.73066-1-dennis@kernel.org/ > > > > Signed-off-by: Dennis Zhou > > Cc: Josef Bacik > > --- > > block/blk-iolatency.c | 17 ++++++----------- > > include/linux/blk_types.h | 12 ++++++++++++ > > 2 files changed, 18 insertions(+), 11 deletions(-) > > > > diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c > > index bee092727cad..52d5d7cc387c 100644 > > --- a/block/blk-iolatency.c > > +++ b/block/blk-iolatency.c > > @@ -463,6 +463,8 @@ static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) > > if (!blk_iolatency_enabled(blkiolat)) > > return; > > > > + bio->bi_start = ktime_get_ns(); > > + > > while (blkg && blkg->parent) { > > struct iolatency_grp *iolat = blkg_to_lat(blkg); > > if (!iolat) { > > @@ -480,18 +482,12 @@ static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) > > } > > > > static void iolatency_record_time(struct iolatency_grp *iolat, > > - struct bio_issue *issue, u64 now, > > + struct bio *bio, u64 now, > > bool issue_as_root) > > { > > - u64 start = bio_issue_time(issue); > > + u64 start = bio->bi_start; > > u64 req_time; > > > > - /* > > - * Have to do this so we are truncated to the correct time that our > > - * issue is truncated to. > > - */ > > - now = __bio_issue_time(now); > > - > > if (now <= start) > > return; > > > > @@ -593,7 +589,7 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) > > bool enabled = false; > > > > blkg = bio->bi_blkg; > > - if (!blkg) > > + if (!blkg || !bio->bi_start) > > return; > > > > iolat = blkg_to_lat(bio->bi_blkg); > > @@ -612,8 +608,7 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) > > atomic_dec(&rqw->inflight); > > if (!enabled || iolat->min_lat_nsec == 0) > > goto next; > > - iolatency_record_time(iolat, &bio->bi_issue, now, > > - issue_as_root); > > + iolatency_record_time(iolat, bio, now, issue_as_root); > > window_start = atomic64_read(&iolat->window_start); > > if (now > window_start && > > (now - window_start) >= iolat->cur_win_nsec) { > > diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h > > index 46c005d601ac..c2c02ec08d7c 100644 > > --- a/include/linux/blk_types.h > > +++ b/include/linux/blk_types.h > > @@ -181,6 +181,18 @@ struct bio { > > */ > > struct blkcg_gq *bi_blkg; > > struct bio_issue bi_issue; > > +#ifdef CONFIG_BLK_CGROUP_IOLATENCY > > + /* > > + * blk-iolatency measure the time a bio takes between rq_qos_throttle() > > + * and rq_qos_done_bio(). It attributes the time to the bio that gets > > + * the request allowing any bios that can tag along via plug merging or > > + * bio merging to be free (from blk-iolatency's perspective). This is > > + * different from the time a bio takes from generic_make_request() to > > + * the end of its life. So, this also serves as a marker for which bios > > + * should be processed by blk-iolatency. > > + */ > > + u64 bi_start; > > +#endif /* CONFIG_BLK_CGROUP_IOLATENCY */ > > So now we have bi_issue and bi_start, both count basically the same thing. Does > using bi_issue actually matter? I assume that it's going to be basically the > same as bi_start for the most part, you are just getting us to only care about > the bio's that we care about. > > What if we just add a bio flag to indicate that we've gone through io-latency? > Once that's in place do these problems go away? Or is the extra time counted > from make_request_time to rq_qos_throttle() actually matter? I feel like it > shouldn't since it's mostly just checks, but I could be mistaken. Thanks, Yeah after talking with Jens about this, it sounds like a good way forward would be to reuse BIO_QUEUE_ENTERED. My initial concern with the flag only approach was the time of stacked drivers. But as they should not be calling into blk_mq_make_request(), tagging in that function should allow us to properly ignore them. It sounds like in the general case where a bio does make it to blk_mq_make_request(), the overhead of the checks prior should be minimal. I'll have a v2 out soon doing tagging with BIO_QUEUE_ENTERED. Thanks, Dennis