Re: [PATCH v3 2/9] ide: Do not set the RQF_PREEMPT flag for sense requests

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 11/23/20 4:17 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.

This patch is a first step towards removing the PREEMPT flag from the
block layer.

Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Can Guo <cang@xxxxxxxxxxxxxx>
Cc: Stanley Chu <stanley.chu@xxxxxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
  drivers/ide/ide-atapi.c | 1 -
  1 file changed, 1 deletion(-)

diff --git a/drivers/ide/ide-atapi.c b/drivers/ide/ide-atapi.c
index 2162bc80f09e..013ad33fbbc8 100644
--- a/drivers/ide/ide-atapi.c
+++ b/drivers/ide/ide-atapi.c
@@ -223,7 +223,6 @@ void ide_prep_sense(ide_drive_t *drive, struct request *rq)
  	sense_rq->rq_disk = rq->rq_disk;
  	sense_rq->cmd_flags = REQ_OP_DRV_IN;
  	ide_req(sense_rq)->type = ATA_PRIV_SENSE;
-	sense_rq->rq_flags |= RQF_PREEMPT;
req->cmd[0] = GPCMD_REQUEST_SENSE;
  	req->cmd[4] = cmd_len;

Reviewed-by: Hannes Reinecke <hare@xxxxxxx>

Cheers,

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




[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [SCSI Target Devel]     [Linux SCSI Target Infrastructure]     [Kernel Newbies]     [IDE]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux ATA RAID]     [Linux IIO]     [Samba]     [Device Mapper]

  Powered by Linux