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Date: Sat, 03 Oct 2009 08:31:06 +0200
From: Mike Galbraith <efault@....de>
To: Jens Axboe <jens.axboe@...cle.com>
Cc: Ingo Molnar <mingo@...e.hu>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Vivek Goyal <vgoyal@...hat.com>,
Ulrich Lukas <stellplatz-nr.13a@...enparkplatz.de>,
linux-kernel@...r.kernel.org,
containers@...ts.linux-foundation.org, dm-devel@...hat.com,
nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
mikew@...gle.com, fchecconi@...il.com, paolo.valente@...more.it,
ryov@...inux.co.jp, fernando@....ntt.co.jp, jmoyer@...hat.com,
dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
righi.andrea@...il.com, m-ikeda@...jp.nec.com, agk@...hat.com,
akpm@...ux-foundation.org, peterz@...radead.org,
jmarchan@...hat.com, riel@...hat.com
Subject: tweaking IO latency [was Re: IO scheduler based IO controller V10]
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 <efault@....de>
> Cc: Jens Axboe <jens.axboe@...cle.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ... 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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