[Devel] [PATCH rh7] mm/page_alloc: use sched_clock() instead of jiffies to measure latency

[Andrey Ryabinin]

sched_clock() (which is rdtsc() on x86) gives us more precise result
than jiffies.

https://pmc.acronis.com/browse/VSTOR-19040
Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
---
 mm/page_alloc.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 74395116344b..362c2a2235c1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3468,9 +3468,11 @@ static void __alloc_collect_stats(gfp_t gfp_mask, 
unsigned int order,
 {
 #ifdef CONFIG_VE
        unsigned long flags;
+       u64 current_clock, delta;
        int ind, cpu;
 
-       time = jiffies_to_usecs(jiffies - time) * 1000;
+       current_clock = sched_clock();
+       delta = current_clock - time;
        if (!(gfp_mask & __GFP_WAIT)) {
                if (in_task())
                        ind = KSTAT_ALLOCSTAT_ATOMIC;
@@ -3485,12 +3487,12 @@ static void __alloc_collect_stats(gfp_t gfp_mask, 
unsigned int order,
 
        local_irq_save(flags);
        cpu = smp_processor_id();
-       KSTAT_LAT_PCPU_ADD(&kstat_glob.alloc_lat[ind], time);
+       KSTAT_LAT_PCPU_ADD(&kstat_glob.alloc_lat[ind], delta);
 
        if (in_task()) {
-               current->alloc_lat[ind].totlat += time;
+               current->alloc_lat[ind].totlat += delta;
                current->alloc_lat[ind].count++;
-               update_maxlat(&current->alloc_lat[ind], time, jiffies);
+               update_maxlat(&current->alloc_lat[ind], delta, current_clock);
        }
 
        if (!page)
@@ -3545,7 +3547,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
        int migratetype = allocflags_to_migratetype(gfp_mask);
        unsigned int cpuset_mems_cookie;
        int alloc_flags = ALLOC_WMARK_LOW|ALLOC_CPUSET|ALLOC_FAIR;
-       cycles_t start;
+       u64 start;
 
        gfp_mask &= gfp_allowed_mask;
 
@@ -3583,7 +3585,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
                alloc_flags |= ALLOC_CMA;
 #endif
 retry:
-       start = jiffies;
+       start = sched_clock();
        /* First allocation attempt */
        page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
                        zonelist, high_zoneidx, alloc_flags,
-- 
2.19.2

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