From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Martijn Coenen <maco@android.com>,
axboe@kernel.dk, hch@lst.de, ming.lei@redhat.com
Cc: mtk.manpages@gmail.com, narayan@google.com, zezeozue@google.com,
kernel-team@android.com, maco@google.com, bvanassche@acm.org,
Chaitanya.Kulkarni@wdc.com, jaegeuk@kernel.org,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH v4 10/10] loop: Add LOOP_CONFIGURE ioctl
Date: Wed, 6 May 2020 11:44:26 +0200 [thread overview]
Message-ID: <7d73bafe-5228-b02e-5b53-4a41543aebe3@gmail.com> (raw)
In-Reply-To: <20200429140341.13294-11-maco@android.com>
Hi Martijn,
On 4/29/20 4:03 PM, Martijn Coenen wrote:
> This allows userspace to completely setup a loop device with a single
> ioctl, removing the in-between state where the device can be partially
> configured - eg the loop device has a backing file associated with it,
> but is reading from the wrong offset.
>
> Besides removing the intermediate state, another big benefit of this
> ioctl is that LOOP_SET_STATUS can be slow; the main reason for this
> slowness is that LOOP_SET_STATUS(64) calls blk_mq_freeze_queue() to
> freeze the associated queue; this requires waiting for RCU
> synchronization, which I've measured can take about 15-20ms on this
> device on average.
>
> In addition to doing what LOOP_SET_STATUS can do, LOOP_CONFIGURE can
> also be used to:
> - Set the correct block size immediately by setting
> loop_config.block_size (avoids LOOP_SET_BLOCK_SIZE)
> - Explicitly request direct I/O mode by setting LO_FLAGS_DIRECT_IO
> in loop_config.info.lo_flags (avoids LOOP_SET_DIRECT_IO)
> - Explicitly request read-only mode by setting LO_FLAGS_READ_ONLY
> in loop_config.info.lo_flags
>
> Here's setting up ~70 regular loop devices with an offset on an x86
> Android device, using LOOP_SET_FD and LOOP_SET_STATUS:
>
> vsoc_x86:/system/apex # time for i in `seq 30 100`;
> do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done
> 0m03.40s real 0m00.02s user 0m00.03s system
>
> Here's configuring ~70 devices in the same way, but using a modified
> losetup that uses the new LOOP_CONFIGURE ioctl:
>
> vsoc_x86:/system/apex # time for i in `seq 30 100`;
> do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done
> 0m01.94s real 0m00.01s user 0m00.01s system
>
> Signed-off-by: Martijn Coenen <maco@android.com>
Can we have also a patch for the loop.4 manual page please?
Thanks,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2020-05-06 9:44 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-29 14:03 [PATCH v4 00/10] Add a new LOOP_CONFIGURE ioctl Martijn Coenen
2020-04-29 14:03 ` [PATCH v4 01/10] loop: Factor out loop size validation Martijn Coenen
2020-04-29 14:12 ` Ming Lei
2020-05-01 11:33 ` Martijn Coenen
2020-05-01 17:26 ` Christoph Hellwig
2020-04-29 14:03 ` [PATCH v4 02/10] loop: Factor out setting loop device size Martijn Coenen
2020-05-01 17:26 ` Christoph Hellwig
2020-04-29 14:03 ` [PATCH v4 03/10] loop: Switch to set_capacity_revalidate_and_notify() Martijn Coenen
2020-05-01 17:27 ` Christoph Hellwig
2020-04-29 14:03 ` [PATCH v4 04/10] loop: Refactor loop_set_status() size calculation Martijn Coenen
2020-05-01 17:30 ` Christoph Hellwig
2020-05-01 19:33 ` Martijn Coenen
2020-05-06 5:10 ` Christoph Hellwig
2020-05-06 6:03 ` Christoph Hellwig
2020-04-29 14:03 ` [PATCH v4 05/10] loop: Remove figure_loop_size() Martijn Coenen
2020-05-06 6:04 ` Christoph Hellwig
2020-04-29 14:03 ` [PATCH v4 06/10] loop: Factor out configuring loop from status Martijn Coenen
2020-05-06 6:05 ` Christoph Hellwig
2020-04-29 14:03 ` [PATCH v4 07/10] loop: Move loop_set_status_from_info() and friends up Martijn Coenen
2020-05-06 6:06 ` Christoph Hellwig
2020-04-29 14:03 ` [PATCH v4 08/10] loop: Rework lo_ioctl() __user argument casting Martijn Coenen
2020-05-06 6:07 ` Christoph Hellwig
2020-04-29 14:03 ` [PATCH v4 09/10] loop: Clean up LOOP_SET_STATUS lo_flags handling Martijn Coenen
2020-05-06 6:08 ` Christoph Hellwig
2020-04-29 14:03 ` [PATCH v4 10/10] loop: Add LOOP_CONFIGURE ioctl Martijn Coenen
2020-05-06 6:09 ` Christoph Hellwig
2020-05-06 9:55 ` Martijn Coenen
2020-05-06 9:44 ` Michael Kerrisk (man-pages) [this message]
2020-05-06 9:57 ` Martijn Coenen
2020-05-12 6:46 ` Martijn Coenen
2020-05-13 2:29 ` Jens Axboe
2020-05-13 2:30 ` Jens Axboe
2020-05-13 7:07 ` Martijn Coenen
2020-05-13 10:22 ` Christoph Hellwig
2020-05-13 13:49 ` Martijn Coenen
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