lkml.org 
[lkml]   [2010]   [Dec]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[Use cpuops V1 02/11] vmstat: Optimize zone counter modifications through the use of this cpu operations
    this cpu operations can be used to slightly optimize the function. The
    changes will avoid some address calculations and replace them with the
    use of the percpu segment register.

    If one would have this_cpu_inc_return and this_cpu_dec_return then it
    would be possible to optimize inc_zone_page_state and dec_zone_page_state even
    more.

    V1->V2:
    - Fix __dec_zone_state overflow handling
    - Use s8 variables for temporary storage.

    V2->V3:
    - Put __percpu annotations in correct places.

    Reviewed-by: Pekka Enberg <penberg@kernel.org>
    Signed-off-by: Christoph Lameter <cl@linux.com>

    ---
    mm/vmstat.c | 56 ++++++++++++++++++++++++++++++++------------------------
    1 file changed, 32 insertions(+), 24 deletions(-)

    Index: linux-2.6/mm/vmstat.c
    ===================================================================
    --- linux-2.6.orig/mm/vmstat.c 2010-11-29 10:17:28.000000000 -0600
    +++ linux-2.6/mm/vmstat.c 2010-11-29 10:36:16.000000000 -0600
    @@ -167,18 +167,20 @@ static void refresh_zone_stat_thresholds
    void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
    int delta)
    {
    - struct per_cpu_pageset *pcp = this_cpu_ptr(zone->pageset);
    -
    - s8 *p = pcp->vm_stat_diff + item;
    + struct per_cpu_pageset __percpu *pcp = zone->pageset;
    + s8 __percpu *p = pcp->vm_stat_diff + item;
    long x;
    + long t;
    +
    + x = delta + __this_cpu_read(*p);

    - x = delta + *p;
    + t = __this_cpu_read(pcp->stat_threshold);

    - if (unlikely(x > pcp->stat_threshold || x < -pcp->stat_threshold)) {
    + if (unlikely(x > t || x < -t)) {
    zone_page_state_add(x, zone, item);
    x = 0;
    }
    - *p = x;
    + __this_cpu_write(*p, x);
    }
    EXPORT_SYMBOL(__mod_zone_page_state);

    @@ -221,16 +223,19 @@ EXPORT_SYMBOL(mod_zone_page_state);
    */
    void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
    {
    - struct per_cpu_pageset *pcp = this_cpu_ptr(zone->pageset);
    - s8 *p = pcp->vm_stat_diff + item;
    -
    - (*p)++;
    + struct per_cpu_pageset __percpu *pcp = zone->pageset;
    + s8 __percpu *p = pcp->vm_stat_diff + item;
    + s8 v, t;
    +
    + __this_cpu_inc(*p);
    +
    + v = __this_cpu_read(*p);
    + t = __this_cpu_read(pcp->stat_threshold);
    + if (unlikely(v > t)) {
    + s8 overstep = t >> 1;

    - if (unlikely(*p > pcp->stat_threshold)) {
    - int overstep = pcp->stat_threshold / 2;
    -
    - zone_page_state_add(*p + overstep, zone, item);
    - *p = -overstep;
    + zone_page_state_add(v + overstep, zone, item);
    + __this_cpu_write(*p, - overstep);
    }
    }

    @@ -242,16 +247,19 @@ EXPORT_SYMBOL(__inc_zone_page_state);

    void __dec_zone_state(struct zone *zone, enum zone_stat_item item)
    {
    - struct per_cpu_pageset *pcp = this_cpu_ptr(zone->pageset);
    - s8 *p = pcp->vm_stat_diff + item;
    -
    - (*p)--;
    -
    - if (unlikely(*p < - pcp->stat_threshold)) {
    - int overstep = pcp->stat_threshold / 2;
    + struct per_cpu_pageset __percpu *pcp = zone->pageset;
    + s8 __percpu *p = pcp->vm_stat_diff + item;
    + s8 v, t;
    +
    + __this_cpu_dec(*p);
    +
    + v = __this_cpu_read(*p);
    + t = __this_cpu_read(pcp->stat_threshold);
    + if (unlikely(v < - t)) {
    + s8 overstep = t >> 1;

    - zone_page_state_add(*p - overstep, zone, item);
    - *p = overstep;
    + zone_page_state_add(v - overstep, zone, item);
    + __this_cpu_write(*p, overstep);
    }
    }



    \
     
     \ /
      Last update: 2010-12-06 18:21    [W:0.042 / U:0.832 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site