Subject: [linux-audio-dev] [Fwd: [PATCH] latency improvements, one reschedule moved]
From: Jörn Nettingsmeier (nettings_AT_folkwang.uni-essen.de)
Date: Sat Jul 01 2000 - 12:18:53 EEST
this message was just posted to linux-sound.
might be of interest....
Roger Larsson wrote:
>
> Hi Linus, Paul, Benno, ...,
>
> [patch against linux-2.4.0-test3-pre2]
>
> I cleaned up kswapd and moved its reschedule point.
> Disk performance is close to the same.
> Latencies have improved a lot (tested with Bennos latencytest)
>
> * sync is still problematic
> * mmap002 (Quintinela) still gives a 212 ms latency
> (compared to 423 ms for the unpatched...)
> * other disk related latencies are down under 30 ms.
> (streaming read, copy, write)
> * the number of overruns has dropped considerably!
> (running 4 buffers with a deadline of 23 ms)
>
> /RogerL
>
> --
> Home page:
> http://www.norran.net/nra02596/
>
> --------------------------------------------------------------------
> --- linux/mm/vmscan.c.orig Wed May 31 20:13:37 2000
> +++ linux/mm/vmscan.c Sat Jul 1 03:29:00 2000
> @@ -419,6 +419,48 @@
> }
>
> /*
> + * Check if there is any memory pressure (free_pages < pages_low)
> + */
> +static inline int memory_pressure(void)
> +{
> + pg_data_t *pgdat = pgdat_list;
> +
> + do {
> + int i;
> + for(i = 0; i < MAX_NR_ZONES; i++) {
> + zone_t *zone = pgdat->node_zones+ i;
> + if (!zone->size &&
> + zone->free_pages < zone->pages_low)
> + return 1;
> + }
> + pgdat = pgdat->node_next;
> + } while (pgdat);
> +
> + return 0;
> +}
> +
> +/*
> + * Check if there is any memory pressure (free_pages < pages_low)
> + */
> +static inline int keep_kswapd_awake(void)
> +{
> + pg_data_t *pgdat = pgdat_list;
> +
> + do {
> + int i;
> + for(i = 0; i < MAX_NR_ZONES; i++) {
> + zone_t *zone = pgdat->node_zones+ i;
> + if (!zone->size &&
> + zone->zone_wake_kswapd)
> + return 1;
> + }
> + pgdat = pgdat->node_next;
> + } while (pgdat);
> +
> + return 0;
> +}
> +
> +/*
> * We need to make the locks finer granularity, but right
> * now we need this so that we can do page allocations
> * without holding the kernel lock etc.
> @@ -442,7 +484,20 @@
>
> priority = 64;
> do {
> + /* should __GFP_WAIT be checked?
> + * assume not - not WAITING for a free page
> + * let more important task execute before
> + * continuing (Note: kswapd does not use it).
> + */
> + if (current->need_resched) {
> + schedule();
> + /* time has passed - pressure too? */
> + if (!memory_pressure())
> + goto done;
> + }
> +
> while (shrink_mmap(priority, gfp_mask)) {
> + /* check __GFP_WAIT ? see below */
> if (!--count)
> goto done;
> }
> @@ -477,16 +532,21 @@
> if (--swap_count < 0)
> break;
>
> - } while (--priority >= 0);
> + priority--;
> + } while (priority >= 0);
>
> /* Always end on a shrink_mmap.. */
> while (shrink_mmap(0, gfp_mask)) {
> + if (current->need_resched)
> + schedule();
> + if (!memory_pressure())
> + return 1;
> if (!--count)
> goto done;
> }
> /* We return 1 if we are freed some page */
> return (count != FREE_COUNT);
> -
> +
> done:
> return 1;
> }
> @@ -530,29 +590,12 @@
> tsk->flags |= PF_MEMALLOC;
>
> for (;;) {
> - pg_data_t *pgdat;
> - int something_to_do = 0;
> -
> - pgdat = pgdat_list;
> - do {
> - int i;
> - for(i = 0; i < MAX_NR_ZONES; i++) {
> - zone_t *zone = pgdat->node_zones+ i;
> - if (tsk->need_resched)
> - schedule();
> - if (!zone->size || !zone->zone_wake_kswapd)
> - continue;
> - if (zone->free_pages < zone->pages_low)
> - something_to_do = 1;
> - do_try_to_free_pages(GFP_KSWAPD);
> - }
> - pgdat = pgdat->node_next;
> - } while (pgdat);
> -
> - if (!something_to_do) {
> - tsk->state = TASK_INTERRUPTIBLE;
> - interruptible_sleep_on(&kswapd_wait);
> + if (!keep_kswapd_awake()) {
> + tsk->state = TASK_INTERRUPTIBLE;
> + interruptible_sleep_on(&kswapd_wait);
> }
> +
> + do_try_to_free_pages(GFP_KSWAPD);
> }
> }
>
-- Jörn Nettingsmeier Kurfürstenstr. 49 45138 Essen, Germany http://www.folkwang.uni-essen.de/~nettings/
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