On Wed, Jun 25 2008, Jens Axboe wrote: > On Thu, Jun 19 2008, Matthew Wilcox wrote: > > Use the noop elevator by default for drives that do not spin > > > > [Not for applying] > > > > SSDs do not benefit from the elevator. It just wastes precious CPU cycles. > > By selecting the noop elevator by default, we can shave a few microseconds > > off each IO. > > > > I've brazenly stolen sd_vpd_inquiry from mkp's patch here: > > > > http://marc.info/?l=linux-scsi&m=121264354724277&w=2 > > > > No need to have two copies of that ... but this will conflict with his code. > > > > On to the self-criticism: > > > > I don't intend the final version of this patch to include a printk for > > the RPM or even a printk to say we switched IO elevator. I think we're > > too verbose in SCSI as it is. > > > > I think there's an opportunity to improve sd_vpd_inquiry() to remove > > some of the duplicate code between sd_set_elevator() and sd_block_limits, > > but it's not terribly important. > > > > The switching of the elevators isn't particularly nice. I assume that > > elevator_init("noop") cannot fail, which isn't true. It would be nice > > to use the #if 0 block instead, but that causes a null ptr dereference > > inside sysfs -- I suspect something isn't set up correctly. > > I disagree with this approach. For now, lets just add a queue flag that > says the device doesn't have a seek penalty and let the io schedulers do > what they need to avoid that (it'd be a one-liner change to cfq and as). > There's more to io scheduling than just seek reduction, so this is the > wrong direction to take imo. OK, a two liner for CFQ. Something like this would be much better I think - maintain the check in SCSI but flag the queue as seek-free if SSD is detected, and let the lower layer worry about the details. Much cleaner, doesn't allow dirty SCSI fingers where they don't belong. diff --git a/block/blk-settings.c b/block/blk-settings.c index 8dd8641..afbf6e0 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -410,6 +410,18 @@ void blk_queue_update_dma_alignment(struct request_queue *q, int mask) } EXPORT_SYMBOL(blk_queue_update_dma_alignment); +void blk_queue_seek_free(struct request_queue *q, int set) +{ + /* + * initialization stuff, don't worry about concurrency + */ + if (set) + queue_flag_set_unlocked(QUEUE_FLAG_SEEKFREE, q); + else + queue_flag_clear_unlocked(QUEUE_FLAG_SEEKFREE, q); +} +EXPORT_SYMBOL(blk_queue_seek_free); + static int __init blk_settings_init(void) { blk_max_low_pfn = max_low_pfn - 1; diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index d01b411..3f654d9 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1423,7 +1423,8 @@ retry: cfq_init_prio_data(cfqq, ioc); if (is_sync) { - if (!cfq_class_idle(cfqq)) + if (!cfq_class_idle(cfqq) && + !test_bit(QUEUE_FLAG_SEEKFREE, &cfqd->queue->queue_flags)) cfq_mark_cfqq_idle_window(cfqq); cfq_mark_cfqq_sync(cfqq); } @@ -1680,7 +1681,8 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq, /* * Don't idle for async or idle io prio class */ - if (!cfq_cfqq_sync(cfqq) || cfq_class_idle(cfqq)) + if (!cfq_cfqq_sync(cfqq) || cfq_class_idle(cfqq) || + test_bit(QUEUE_FLAG_SEEKFREE, &cfqd->queue->queue_flags)) return; enable_idle = cfq_cfqq_idle_window(cfqq); diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index d2a1b71..8e77cb5 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -409,6 +409,7 @@ struct request_queue #define QUEUE_FLAG_ELVSWITCH 8 /* don't use elevator, just do FIFO */ #define QUEUE_FLAG_BIDI 9 /* queue supports bidi requests */ #define QUEUE_FLAG_NOMERGES 10 /* disable merge attempts */ +#define QUEUE_FLAG_SEEKFREE 11 /* seeks are free */ static inline int queue_is_locked(struct request_queue *q) { @@ -757,6 +758,7 @@ extern void blk_queue_prep_rq(struct request_queue *, prep_rq_fn *pfn); extern void blk_queue_merge_bvec(struct request_queue *, merge_bvec_fn *); extern void blk_queue_dma_alignment(struct request_queue *, int); extern void blk_queue_update_dma_alignment(struct request_queue *, int); +extern void blk_queue_seek_free(struct request_queue *, int); extern void blk_queue_softirq_done(struct request_queue *, softirq_done_fn *); extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev); extern int blk_queue_ordered(struct request_queue *, unsigned, prepare_flush_fn *); -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
