diff options
author | Shaohua Li <shaohua.li@intel.com> | 2009-11-03 20:25:02 +0100 |
---|---|---|
committer | Jens Axboe <jens.axboe@oracle.com> | 2009-11-03 20:25:02 +0100 |
commit | 4b27e1bb442e964903f8a3fa6bdf33a602dc0941 (patch) | |
tree | d7eecb66f6a75dbff292fbd03b643b04ed075289 /block | |
parent | cfq-iosched: fix bad return value cfq_should_preempt() (diff) | |
download | linux-4b27e1bb442e964903f8a3fa6bdf33a602dc0941.tar.xz linux-4b27e1bb442e964903f8a3fa6bdf33a602dc0941.zip |
cfq-iosched: limit coop preemption
CFQ has an optimization for cooperated applications. if several
io-context have close requests, they will get boost. But the
optimization get abused. Considering thread a, b, which work on one
file. a reads sectors s, s+2, s+4, ...; b reads sectors s+1, s+3, s
+5, ... Both a and b are sequential read, so they can open idle window.
a reads a sector s and goes to idle window and wakeup b. b reads sector
s+1, since in current implementation, cfq_should_preempt() thinks a and
b are cooperators, b will preempt a. b then reads sector s+1 and goes to
idle window and wakeup a. for the same reason, a will preempt b and
reads s+2. a and b will continue the circle. The circle will be very
long, and a and b will occupy whole disk queue. Other applications will
nearly have no chance to run.
Fix this limiting coop preempt until a queue is scheduled normally
again.
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'block')
-rw-r--r-- | block/cfq-iosched.c | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 5802e322b7ad..aa1e9535e358 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -196,6 +196,7 @@ enum cfqq_state_flags { CFQ_CFQQ_FLAG_slice_new, /* no requests dispatched in slice */ CFQ_CFQQ_FLAG_sync, /* synchronous queue */ CFQ_CFQQ_FLAG_coop, /* has done a coop jump of the queue */ + CFQ_CFQQ_FLAG_coop_preempt, /* coop preempt */ }; #define CFQ_CFQQ_FNS(name) \ @@ -222,6 +223,7 @@ CFQ_CFQQ_FNS(prio_changed); CFQ_CFQQ_FNS(slice_new); CFQ_CFQQ_FNS(sync); CFQ_CFQQ_FNS(coop); +CFQ_CFQQ_FNS(coop_preempt); #undef CFQ_CFQQ_FNS #define cfq_log_cfqq(cfqd, cfqq, fmt, args...) \ @@ -945,10 +947,13 @@ static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd, { if (!cfqq) { cfqq = cfq_get_next_queue(cfqd); - if (cfqq) + if (cfqq && !cfq_cfqq_coop_preempt(cfqq)) cfq_clear_cfqq_coop(cfqq); } + if (cfqq) + cfq_clear_cfqq_coop_preempt(cfqq); + __cfq_set_active_queue(cfqd, cfqq); return cfqq; } @@ -2066,8 +2071,16 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq, * if this request is as-good as one we would expect from the * current cfqq, let it preempt */ - if (cfq_rq_close(cfqd, rq)) + if (cfq_rq_close(cfqd, rq) && (!cfq_cfqq_coop(new_cfqq) || + cfqd->busy_queues == 1)) { + /* + * Mark new queue coop_preempt, so its coop flag will not be + * cleared when new queue gets scheduled at the very first time + */ + cfq_mark_cfqq_coop_preempt(new_cfqq); + cfq_mark_cfqq_coop(new_cfqq); return true; + } return false; } |