From: Jens Axboe <axboe@kernel.dk>
To: Christoph Hellwig <hch@lst.de>, Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org
Subject: Re: boot stall regression due to blk-mq: use percpu_ref for mq usage count
Date: Fri, 19 Sep 2014 13:13:11 -0600 [thread overview]
Message-ID: <541C8047.80705@kernel.dk> (raw)
In-Reply-To: <20140919113815.GA10791@lst.de>
On 09/19/2014 05:38 AM, Christoph Hellwig wrote:
> Hi Jens, hi Tejun,
>
> I've seen multi-second boot stalls in one of my KVM setups during
> the initial scsi scan:
>
> [ 0.949892] scsi host0: Virtio SCSI HBA
> [ 1.007864] scsi 0:0:0:0: Direct-Access QEMU QEMU HARDDISK 1.1. PQ: 0 ANSI: 5
> [ 1.021299] scsi 0:0:1:0: Direct-Access QEMU QEMU HARDDISK 1.1. PQ: 0 ANSI: 5
> [ 1.520356] tsc: Refined TSC clocksource calibration: 2491.910 MHz
>
> <stall>
>
> [ 16.186549] sd 0:0:0:0: Attached scsi generic sg0 type 0
> [ 16.190478] sd 0:0:1:0: Attached scsi generic sg1 type 0
> [ 16.194099] osd: LOADED open-osd 0.2.1
> [ 16.203202] sd 0:0:0:0: [sda] 31457280 512-byte logical blocks: (16.1 GB/15.0 GiB)
> [ 16.208478] sd 0:0:0:0: [sda] Write Protect is off
> [ 16.211439] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
> [ 16.218771] sd 0:0:1:0: [sdb] 31457280 512-byte logical blocks: (16.1 GB/15.0 GiB)
> [ 16.223264] sd 0:0:1:0: [sdb] Write Protect is off
> [ 16.225682] sd 0:0:1:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
>
>
>
> I've tracked this down to "blk-mq: use percpu_ref for mq usage count" in
> a rather painful way as that one introduced enough other regressions
> to mess up bisect.
>
> If I revert the following commits:
>
> dd840087086f3b93ac20f7472b4fca59aff7b79f
> cddd5d17642cc6881352732693c2ae6930e9ce65
> add703fda981b9719d37f371498b9f129acbd997
>
> which are the above mentioned commit and two fixes to it the problem goes
> away.
Thanks for bisecting this, I ran into something that I think is the same
issue about a week ago. Tejun, any ideas before I dig into this one?
--
Jens Axboe
next prev parent reply other threads:[~2014-09-19 19:12 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-19 11:38 boot stall regression due to blk-mq: use percpu_ref for mq usage count Christoph Hellwig
2014-09-19 19:13 ` Jens Axboe [this message]
2014-09-23 5:55 ` Christoph Hellwig
2014-09-23 5:56 ` Tejun Heo
2014-09-23 5:57 ` Tejun Heo
2014-09-23 5:59 ` Christoph Hellwig
2014-09-23 6:01 ` Tejun Heo
2014-09-23 6:03 ` Tejun Heo
2014-09-23 6:09 ` Christoph Hellwig
2014-09-23 6:11 ` Tejun Heo
2014-09-23 14:57 ` Elliott, Robert (Server Storage)
2014-09-23 15:49 ` Jens Axboe
2014-09-23 19:24 ` [PATCH block/for-3.17-fixes/core] blk-mq, percpu_ref: implement a kludge for SCSI blk-mq stall during probe Tejun Heo
2014-09-23 19:29 ` Jens Axboe
2014-09-23 19:48 ` Tejun Heo
2014-09-24 8:23 ` Christoph Hellwig
2014-09-24 14:30 ` Jens Axboe
2014-09-24 14:33 ` Tejun Heo
2014-09-24 14:33 ` Jens Axboe
2014-09-24 17:20 ` [PATCH percpu/for-3.18] Revert "blk-mq, percpu_ref: implement a kludge for SCSI blk-mq stall during probe" Tejun Heo
2014-09-23 6:08 ` [PATCH block/for-3.18/core] blk-mq: start q->mq_usage_counter in atomic mode Tejun Heo
2014-09-24 17:33 ` Tejun Heo
2014-09-24 17:43 ` [PATCH percpu/for-3.18] blk-mq, percpu_ref: " Tejun Heo
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