P.S. now may be a good time to finally exit thread (and maybe trim cc?) On Sat, 2009-10-03 at 07:56 +0200, Mike Galbraith wrote: > On Sat, 2009-10-03 at 07:49 +0200, Mike Galbraith wrote: > > On Fri, 2009-10-02 at 20:19 +0200, Jens Axboe wrote: > > > > > If you could do a cleaned up version of your overload patch based on > > > this: > > > > > > http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=1d2235152dc745c6d94bedb550fea84cffdbf768 > > > > > > then lets take it from there. > > Note to self: build the darn thing after last minute changes. > > Block: Delay overloading of CFQ queues to improve read latency. > > Introduce a delay maximum dispatch timestamp, and stamp it when: > 1. we encounter a known seeky or possibly new sync IO queue. > 2. the current queue may go idle and we're draining async IO. > 3. we have sync IO in flight and are servicing an async queue. > 4 we are not the sole user of disk. > Disallow exceeding quantum if any of these events have occurred recently. > > Protect this behavioral change with a "desktop_dispatch" knob and default > it to "on".. providing an easy means of regression verification prior to > hate-mail dispatch :) to CC list. > > Signed-off-by: Mike Galbraith <[email protected]> > Cc: Jens Axboe <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Andrew Morton <[email protected]> > ... others who let somewhat hacky tweak slip by > > --- > block/cfq-iosched.c | 45 +++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 41 insertions(+), 4 deletions(-) > > Index: linux-2.6/block/cfq-iosched.c > =================================================================== > --- linux-2.6.orig/block/cfq-iosched.c > +++ linux-2.6/block/cfq-iosched.c > @@ -174,6 +174,9 @@ struct cfq_data { > unsigned int cfq_slice_async_rq; > unsigned int cfq_slice_idle; > unsigned int cfq_desktop; > + unsigned int cfq_desktop_dispatch; > + > + unsigned long desktop_dispatch_ts; > > struct list_head cic_list; > > @@ -1283,6 +1286,7 @@ static int cfq_dispatch_requests(struct > struct cfq_data *cfqd = q->elevator->elevator_data; > struct cfq_queue *cfqq; > unsigned int max_dispatch; > + unsigned long delay; > > if (!cfqd->busy_queues) > return 0; > @@ -1297,19 +1301,26 @@ static int cfq_dispatch_requests(struct > /* > * Drain async requests before we start sync IO > */ > - if (cfq_cfqq_idle_window(cfqq) && cfqd->rq_in_driver[BLK_RW_ASYNC]) > + if (cfq_cfqq_idle_window(cfqq) && cfqd->rq_in_driver[BLK_RW_ASYNC]) { > + cfqd->desktop_dispatch_ts = jiffies; > return 0; > + } > > /* > * If this is an async queue and we have sync IO in flight, let it wait > */ > - if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq)) > + if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq)) { > + cfqd->desktop_dispatch_ts = jiffies; > return 0; > + } > > max_dispatch = cfqd->cfq_quantum; > if (cfq_class_idle(cfqq)) > max_dispatch = 1; > > + if (cfqd->busy_queues > 1) > + cfqd->desktop_dispatch_ts = jiffies; > + > /* > * Does this cfqq already have too much IO in flight? > */ > @@ -1327,6 +1338,16 @@ static int cfq_dispatch_requests(struct > return 0; > > /* > + * Don't start overloading until we've been alone for a bit. > + */ > + if (cfqd->cfq_desktop_dispatch) { > + delay = cfqd->desktop_dispatch_ts + cfq_slice_sync; > + > + if (time_before(jiffies, max_delay)) > + return 0; > + } > + > + /* > * we are the only queue, allow up to 4 times of 'quantum' > */ > if (cfqq->dispatched >= 4 * max_dispatch) > @@ -1942,7 +1963,7 @@ static void > cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq, > struct cfq_io_context *cic) > { > - int old_idle, enable_idle; > + int old_idle, enable_idle, seeky = 0; > > /* > * Don't idle for async or idle io prio class > @@ -1950,10 +1971,20 @@ cfq_update_idle_window(struct cfq_data * > if (!cfq_cfqq_sync(cfqq) || cfq_class_idle(cfqq)) > return; > > + if (cfqd->hw_tag) { > + if (CIC_SEEKY(cic)) > + seeky = 1; > + /* > + * If seeky or incalculable seekiness, delay overloading. > + */ > + if (seeky || !sample_valid(cic->seek_samples)) > + cfqd->desktop_dispatch_ts = jiffies; > + } > + > enable_idle = old_idle = cfq_cfqq_idle_window(cfqq); > > if (!atomic_read(&cic->ioc->nr_tasks) || !cfqd->cfq_slice_idle || > - (!cfqd->cfq_desktop && cfqd->hw_tag && CIC_SEEKY(cic))) > + (!cfqd->cfq_desktop && seeky)) > enable_idle = 0; > else if (sample_valid(cic->ttime_samples)) { > if (cic->ttime_mean > cfqd->cfq_slice_idle) > @@ -2483,6 +2514,9 @@ static void *cfq_init_queue(struct reque > cfqd->cfq_slice_async_rq = cfq_slice_async_rq; > cfqd->cfq_slice_idle = cfq_slice_idle; > cfqd->cfq_desktop = 1; > + cfqd->cfq_desktop_dispatch = 1; > + > + cfqd->desktop_dispatch_ts = INITIAL_JIFFIES; > cfqd->hw_tag = 1; > > return cfqd; > @@ -2553,6 +2587,7 @@ SHOW_FUNCTION(cfq_slice_sync_show, cfqd- > SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1); > SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0); > SHOW_FUNCTION(cfq_desktop_show, cfqd->cfq_desktop, 0); > +SHOW_FUNCTION(cfq_desktop_dispatch_show, cfqd->cfq_desktop_dispatch, 0); > #undef SHOW_FUNCTION > > #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) > \ > @@ -2585,6 +2620,7 @@ STORE_FUNCTION(cfq_slice_async_store, &c > STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1, > UINT_MAX, 0); > STORE_FUNCTION(cfq_desktop_store, &cfqd->cfq_desktop, 0, 1, 0); > +STORE_FUNCTION(cfq_desktop_dispatch_store, &cfqd->cfq_desktop_dispatch, 0, > 1, 0); > #undef STORE_FUNCTION > > #define CFQ_ATTR(name) \ > @@ -2601,6 +2637,7 @@ static struct elv_fs_entry cfq_attrs[] = > CFQ_ATTR(slice_async_rq), > CFQ_ATTR(slice_idle), > CFQ_ATTR(desktop), > + CFQ_ATTR(desktop_dispatch), > __ATTR_NULL > }; > >
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