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From: Hannes Reinecke <hare@suse.de>
To: Bart Van Assche <bvanassche@acm.org>,
	"Martin K . Petersen" <martin.petersen@oracle.com>
Cc: "James E . J . Bottomley" <jejb@linux.vnet.ibm.com>,
	Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
	Ming Lei <ming.lei@redhat.com>,
	linux-scsi@vger.kernel.org, linux-block@vger.kernel.org,
	"David S . Miller" <davem@davemloft.net>,
	Alan Stern <stern@rowland.harvard.edu>,
	Can Guo <cang@codeaurora.org>,
	Stanley Chu <stanley.chu@mediatek.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>
Subject: Re: [PATCH v4 3/9] ide: Do not set the RQF_PREEMPT flag for sense requests
Date: Wed, 2 Dec 2020 07:52:41 +0100	[thread overview]
Message-ID: <f526d625-6be2-d3ee-5d3d-2f2543e8ffd9@suse.de> (raw)
In-Reply-To: <20201130024615.29171-4-bvanassche@acm.org>

On 11/30/20 3:46 AM, Bart Van Assche wrote:
> RQF_PREEMPT is used for two different purposes in the legacy IDE code:
> 1. To mark power management requests.
> 2. To mark requests that should preempt another request. An (old)
>     explanation of that feature is as follows:
>     "The IDE driver in the Linux kernel normally uses a series of busywait
>     delays during its initialization. When the driver executes these
>     busywaits, the kernel does nothing for the duration of the wait. The
>     time spent in these waits could be used for other initialization
>     activities, if they could be run concurrently with these waits.
> 
>     More specifically, busywait-style delays such as udelay() in module
>     init functions inhibit kernel preemption because the Big Kernel Lock
>     is held, while yielding APIs such as schedule_timeout() allow
>     preemption. This is true because the kernel handles the BKL specially
>     and releases and reacquires it across reschedules allowed by the
>     current thread.
> 
>     This IDE-preempt specification requires that the driver eliminate these
>     busywaits and replace them with a mechanism that allows other work to
>     proceed while the IDE driver is initializing."
> 
> Since I haven't found an implementation of (2), do not set the PREEMPT
> flag for sense requests. This patch causes sense requests to be
> postponed while a drive is suspended instead of being submitted to
> ide_queue_rq().
> 
> If it would ever be necessary to restore the IDE PREEMPT functionality,
> that can be done by introducing a new flag in struct ide_request.
> 
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Cc: Can Guo <cang@codeaurora.org>
> Cc: Stanley Chu <stanley.chu@mediatek.com>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>   drivers/ide/ide-atapi.c | 1 -
>   drivers/ide/ide-io.c    | 5 -----
>   2 files changed, 6 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

  parent reply	other threads:[~2020-12-02  6:53 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-30  2:46 [PATCH v4 0/9] Rework runtime suspend and SPI domain validation Bart Van Assche
2020-11-30  2:46 ` [PATCH v4 1/9] block: Fix a race in the runtime power management code Bart Van Assche
2020-11-30  2:46 ` [PATCH v4 2/9] block: Introduce BLK_MQ_REQ_PM Bart Van Assche
2020-12-01 11:31   ` Christoph Hellwig
2020-12-02  6:50   ` Hannes Reinecke
2020-11-30  2:46 ` [PATCH v4 3/9] ide: Do not set the RQF_PREEMPT flag for sense requests Bart Van Assche
2020-12-01 11:29   ` Christoph Hellwig
2020-12-02  6:52   ` Hannes Reinecke [this message]
2020-11-30  2:46 ` [PATCH v4 4/9] ide: Mark power management requests with RQF_PM instead of RQF_PREEMPT Bart Van Assche
2020-12-01 11:31   ` Christoph Hellwig
2020-12-02  6:53   ` Hannes Reinecke
2020-11-30  2:46 ` [PATCH v4 5/9] scsi: Do not wait for a request in scsi_eh_lock_door() Bart Van Assche
2020-12-02  7:06   ` Hannes Reinecke
2020-12-03  5:10     ` Bart Van Assche
2020-12-03  7:18       ` Hannes Reinecke
2020-12-03  7:27         ` Ming Lei
2020-12-04 16:50           ` Bart Van Assche
2020-11-30  2:46 ` [PATCH v4 6/9] scsi_transport_spi: Set RQF_PM for domain validation commands Bart Van Assche
2020-12-01 11:31   ` Christoph Hellwig
2020-11-30  2:46 ` [PATCH v4 7/9] scsi: Only process PM requests if rpm_status != RPM_ACTIVE Bart Van Assche
2020-12-01 11:32   ` Christoph Hellwig
2020-12-02  7:14   ` Hannes Reinecke
2020-11-30  2:46 ` [PATCH v4 8/9] block: Remove RQF_PREEMPT and BLK_MQ_REQ_PREEMPT Bart Van Assche
2020-12-01 11:33   ` Christoph Hellwig
2020-12-02  7:15   ` Hannes Reinecke
2020-11-30  2:46 ` [PATCH v4 9/9] block: Do not accept any requests while suspended Bart Van Assche
2020-12-02  7:16   ` Hannes Reinecke
2020-12-02  1:51 ` [PATCH v4 0/9] Rework runtime suspend and SPI domain validation Martin K. Petersen
2020-12-06  0:01   ` Jens Axboe
2020-12-08  1:56 ` Martin K. Petersen

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