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SubjectRe: [PATCH 1/2] don't wait on disk to start on resume
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Missing cc to linux-scsi added 

On Thu, 2012-12-20 at 20:35 -0800, Derek Basehore wrote:
> We no longer wait for the disk to spin up in sd_resume. It now enters the
> request to spinup the disk into the elevator and returns.
>
> A function is scheduled under the scsi_sd_probe_domain to wait for the command
> to spinup the disk to complete. This function then checks for errors and cleans
> up after the sd resume function.
>
> This allows system resume to complete much faster on systems with an HDD since
> spinning up the disk is a significant portion of resume time.
>
> Signed-off-by: Derek Basehore <dbasehore@chromium.org>
> ---
> drivers/scsi/sd.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++++---
> drivers/scsi/sd.h | 9 ++++
> 2 files changed, 108 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 7992635..2fe051f 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -3045,6 +3045,7 @@ static void sd_shutdown(struct device *dev)
> if (!sdkp)
> return; /* this can happen */
>
> + async_synchronize_full_domain(&scsi_sd_probe_domain);

What's the point of this? We already have one in sd_remove() which is
the correct last callback.

> if (pm_runtime_suspended(dev))
> goto exit;
>
> @@ -3070,6 +3071,7 @@ static int sd_suspend(struct device *dev)
> if (!sdkp)
> return 0; /* this can happen */
>
> + async_synchronize_full_domain(&scsi_sd_probe_domain);
> if (sdkp->WCE) {
> sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n");
> ret = sd_sync_cache(sdkp);
> @@ -3087,20 +3089,110 @@ done:
> return ret;
> }
>
> +/*
> + * Callback function for when the request that starts the disk completes. Passed
> + * into blk_execute_rq_nowait in sd_resume.
> + */
> +static void sd_end_start_rq(struct request *rq, int error)
> +{
> + struct completion *waiting = rq->end_io_data;
> +
> + rq->end_io_data = NULL;
> + /*
> + * Set the end_io_data to NULL before calling complete. This (with
> + * sd_resume async) ensures that it is set to NULL before we call
> + * blk_put_request.
> + */
> + complete(waiting);
> +}
> +
> +/*
> + * Asynchronous part of sd_resume. This is separate from sd_end_start_rq since
> + * we need to block on resume for suspend and shutdown. We already do this by
> + * synchronizing on the scsi_sd_probe_domain, so use that.
> + */
> +static void sd_resume_async(void *data, async_cookie_t cookie)
> +{
> + struct scsi_sense_hdr sshdr;
> + struct resume_async_struct *resume = data;
> + struct scsi_disk *sdkp = resume->sdkp;
> + struct request *req = resume->req;
> +
> + wait_for_completion(&resume->wait);
> +
> + if (req->errors) {
> + scsi_normalize_sense(resume->sense,
> + SCSI_SENSE_BUFFERSIZE,
> + &sshdr);
> + sd_printk(KERN_WARNING, sdkp, "START_STOP FAILED\n");
> + sd_print_result(sdkp, req->errors);
> + if (driver_byte(req->errors) & DRIVER_SENSE)
> + sd_print_sense_hdr(sdkp, &sshdr);
> + }
> + kfree(resume);
> + scsi_disk_put(sdkp);
> + blk_put_request(req);
> +}
> +
> +/*
> + * This does not wait for the disk to spin up. This function enters the request
> + * to spinup the disk and schedules a function, sd_resume_async, that waits for
> + * that request to complete.
> + */
> static int sd_resume(struct device *dev)
> {
> struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
> - int ret = 0;
> + struct scsi_device *sdp = sdkp->device;
> + struct resume_async_struct *resume = NULL;
> + struct request *req;
> + unsigned char cmd[6] = { START_STOP }; /* START_VALID */
>
> - if (!sdkp->device->manage_start_stop)
> - goto done;
> + if (!sdkp->device->manage_start_stop) {
> + scsi_disk_put(sdkp);
> + return 0;
> + }
>
> sd_printk(KERN_NOTICE, sdkp, "Starting disk\n");
> - ret = sd_start_stop_device(sdkp, 1);
>
> -done:
> - scsi_disk_put(sdkp);
> - return ret;
> + cmd[4] |= 1; /* START */
> +
> + if (sdp->start_stop_pwr_cond)
> + cmd[4] |= 1 << 4; /* Active */
> +
> + if (!scsi_device_online(sdp))
> + return -ENODEV;
> +
> + resume = kzalloc(sizeof(struct resume_async_struct), GFP_NOIO);
> + if (!resume)
> + return DRIVER_ERROR << 24;
> +
> + req = blk_get_request(sdp->request_queue, 0, __GFP_WAIT);
> + if (!req)
> + return DRIVER_ERROR << 24;
> +
> + resume->req = req;
> + resume->sdkp = sdkp;
> + init_completion(&resume->wait);
> +
> + req->cmd_len = COMMAND_SIZE(cmd[0]);
> + memcpy(req->cmd, cmd, req->cmd_len);
> + req->sense = resume->sense;
> + req->sense_len = 0;
> + req->retries = SD_MAX_RETRIES;
> + req->timeout = SD_TIMEOUT;
> + req->cmd_type = REQ_TYPE_BLOCK_PC;
> + req->cmd_flags |= REQ_QUIET | REQ_PREEMPT;
> + req->end_io_data = &resume->wait;
> +
> + async_schedule_domain(sd_resume_async, resume, &scsi_sd_probe_domain);
> + /*
> + * don't wait here for the disk to spin up, since we can resume faster
> + * if we don't. Cleanup and checking for errors is done the the
> + * previously scheduled sd_resume_async function
> + */
> + blk_execute_rq_nowait(req->q, NULL, req, 1, sd_end_start_rq);

What is the point of open coding sd_start_stop_device() instead of just
calling it in the async function?

> +
> + return 0;
> }
>
> /**
> diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
> index 74a1e4c..b09f255 100644
> --- a/drivers/scsi/sd.h
> +++ b/drivers/scsi/sd.h
> @@ -1,6 +1,8 @@
> #ifndef _SCSI_DISK_H
> #define _SCSI_DISK_H
>
> +#include <scsi/scsi_cmnd.h>
> +
> /*
> * More than enough for everybody ;) The huge number of majors
> * is a leftover from 16bit dev_t days, we don't really need that
> @@ -87,6 +89,13 @@ struct scsi_disk {
> };
> #define to_scsi_disk(obj) container_of(obj,struct scsi_disk,dev)
>
> +struct resume_async_struct {
> + struct scsi_disk *sdkp;
> + struct request *req;
> + struct completion wait;
> + char sense[SCSI_SENSE_BUFFERSIZE];
> +};

If you don't open code sd_start_stop_device() you don't need any of this
because you don't pass information around to async functions.

James

> static inline struct scsi_disk *scsi_disk(struct gendisk *disk)
> {
> return container_of(disk->private_data, struct scsi_disk, driver);




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