diff options
Diffstat (limited to 'block/bfq-iosched.c')
| -rw-r--r-- | block/bfq-iosched.c | 26 |
1 files changed, 15 insertions, 11 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 21011019f5df..128b3be49463 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -876,22 +876,26 @@ static unsigned int bfq_wr_duration(struct bfq_data *bfqd) do_div(dur, bfqd->peak_rate); /* - * Limit duration between 3 and 13 seconds. Tests show that - * higher values than 13 seconds often yield the opposite of - * the desired result, i.e., worsen responsiveness by letting - * non-interactive and non-soft-real-time applications - * preserve weight raising for a too long time interval. + * Limit duration between 3 and 25 seconds. The upper limit + * has been conservatively set after the following worst case: + * on a QEMU/KVM virtual machine + * - running in a slow PC + * - with a virtual disk stacked on a slow low-end 5400rpm HDD + * - serving a heavy I/O workload, such as the sequential reading + * of several files + * mplayer took 23 seconds to start, if constantly weight-raised. + * + * As for higher values than that accomodating the above bad + * scenario, tests show that higher values would often yield + * the opposite of the desired result, i.e., would worsen + * responsiveness by allowing non-interactive applications to + * preserve weight raising for too long. * * On the other end, lower values than 3 seconds make it * difficult for most interactive tasks to complete their jobs * before weight-raising finishes. */ - if (dur > msecs_to_jiffies(13000)) - dur = msecs_to_jiffies(13000); - else if (dur < msecs_to_jiffies(3000)) - dur = msecs_to_jiffies(3000); - - return dur; + return clamp_val(dur, msecs_to_jiffies(3000), msecs_to_jiffies(25000)); } /* switch back from soft real-time to interactive weight raising */ |