| Message ID | 20201123031749.14912-3-bvanassche@acm.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Rework runtime suspend and SCSI domain validation | expand |
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@lst.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 - > 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@suse.de> Cheers, Hannes
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;