On 10/25/2017 05:52 AM, Douglas Gilbert wrote:
> The sd_setup_read_write_cmnd() function is on the "fast path" for
> block system access to SCSI devices (logical units). Rewrite this
> function to improve speed and readability:
> - use put_unaligned_be family of functions to save lots of shifts
> - improve the scaling code when sector_size > 512 bytes
> - use variable names containing "sect" for block system quantities
> which have implicit 512 byte sector size. Use "lba" and
> "num_blks" after optional scaling to match the logical block
> address and number of logical blocks of the SCSI device being
> accessed
> - use local variables to hold values that were previously calculated
> more than once
>
> Signed-off-by: Douglas Gilbert <dgilb...@interlog.com>
> ---
> drivers/scsi/sd.c | 216
> ++++++++++++++++++++++++------------------------------
> 1 file changed, 94 insertions(+), 122 deletions(-)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index d175c5c5ccf8..618cb5d0f75a 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -1004,11 +1004,18 @@ static int sd_setup_read_write_cmnd(struct scsi_cmnd
> *SCpnt)
> struct scsi_device *sdp = SCpnt->device;
> struct gendisk *disk = rq->rq_disk;
> struct scsi_disk *sdkp = scsi_disk(disk);
> - sector_t block = blk_rq_pos(rq);
> - sector_t threshold;
> - unsigned int this_count = blk_rq_sectors(rq);
> + unsigned int num_sects = blk_rq_sectors(rq);
> + unsigned int num_blks;
> unsigned int dif, dix;
> - bool zoned_write = sd_is_zoned(sdkp) && rq_data_dir(rq) == WRITE;
> + unsigned int sect_sz;
> + sector_t sect_addr = blk_rq_pos(rq);
> + sector_t sect_after = sect_addr + num_sects;
> + sector_t total_sects = get_capacity(disk);
> + sector_t threshold_sect;
> + sector_t lba;
> + bool is_write = (rq_data_dir(rq) == WRITE);
> + bool have_fua = !!(rq->cmd_flags & REQ_FUA);
> + bool zoned_write = sd_is_zoned(sdkp) && is_write;
> int ret;
> unsigned char protect;
>
> @@ -1029,20 +1036,23 @@ static int sd_setup_read_write_cmnd(struct scsi_cmnd
> *SCpnt)
>
> SCSI_LOG_HLQUEUE(1,
> scmd_printk(KERN_INFO, SCpnt,
> - "%s: block=%llu, count=%d\n",
> - __func__, (unsigned long long)block, this_count));
> + "%s: sector=%llu, num_sects=%d\n",
> + __func__, (unsigned long long)sect_addr, num_sects));
>
> - if (!sdp || !scsi_device_online(sdp) ||
> - block + blk_rq_sectors(rq) > get_capacity(disk)) {
> + if (likely(sdp && scsi_device_online(sdp) &&
> + (sect_after <= total_sects)))
> + ; /* ok: have device, its online and access fits on medium */
> + else {
> SCSI_LOG_HLQUEUE(2, scmd_printk(KERN_INFO, SCpnt,
> "Finishing %u sectors\n",
> - blk_rq_sectors(rq)));
> + num_sects));
> SCSI_LOG_HLQUEUE(2, scmd_printk(KERN_INFO, SCpnt,
> "Retry with 0x%p\n", SCpnt));
> goto out;
> }
> + sect_sz = sdp->sector_size;
>
> - if (sdp->changed) {
> + if (unlikely(sdp->changed)) {
> /*
> * quietly refuse to do anything to a changed disc until
> * the changed bit has been reset
Please invert the 'if' condition to avoid the empty branch.
> @@ -1055,21 +1065,22 @@ static int sd_setup_read_write_cmnd(struct scsi_cmnd
> *SCpnt)
> * Some SD card readers can't handle multi-sector accesses which touch
> * the last one or two hardware sectors. Split accesses as needed.
> */
> - threshold = get_capacity(disk) - SD_LAST_BUGGY_SECTORS *
> - (sdp->sector_size / 512);
> -
> - if (unlikely(sdp->last_sector_bug && block + this_count > threshold)) {
> - if (block < threshold) {
> - /* Access up to the threshold but not beyond */
> - this_count = threshold - block;
> - } else {
> - /* Access only a single hardware sector */
> - this_count = sdp->sector_size / 512;
> - }
> + if (unlikely(sdp->last_sector_bug)) {
> + threshold_sect = total_sects -
> + (SD_LAST_BUGGY_SECTORS * (sect_sz / 512));
> +
> + if (unlikely(sect_after > threshold_sect))
> + num_sects = (sect_addr < threshold_sect) ?
> + (threshold_sect - sect_addr) :
> + (sect_sz / 512);
> + /* If LBA less than threshold then access up to the
> + * threshold but not beyond; otherwise access only
> + * a single hardware sector.
> + */
> }
>
> - SCSI_LOG_HLQUEUE(2, scmd_printk(KERN_INFO, SCpnt, "block=%llu\n",
> - (unsigned long long)block));
> + SCSI_LOG_HLQUEUE(2, scmd_printk(KERN_INFO, SCpnt, "num_sects=%llu\n",
> + (unsigned long long)num_sects));
>
> /*
> * If we have a 1K hardware sectorsize, prevent access to single
Why did you change the log message?
I'd rather keep it as it were...
Cheers,
Hannes
--
--
Dr. Hannes Reinecke Teamlead Storage & Networking
h...@suse.de +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
