linux-kernel - Re: [External] Re: mm/cma.c: High latency for cma allocation

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Message-ID: <20190321095337.GM8696@dhcp22.suse.cz>
Date:   Thu, 21 Mar 2019 10:53:37 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Pankaj Suryawanshi <pankaj.suryawanshi@...fochips.com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "minchan@...nel.org" <minchan@...nel.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>
Subject: Re: [External] Re: mm/cma.c: High latency for cma allocation

Can you please fix your email client? The broken quoting is just
irritating.

On Tue 19-03-19 11:45:03, Pankaj Suryawanshi wrote:
[...]
> I have tried for latency count for 385MB:
> 
> reclaim- reclaim_clean_pages_from_list()
> migrate- migrate_pages()
> migrateranges- isolate_migratepages_range()
> overall - __alloc_contig_migrate_range()
> 
> Note: output is in us
> 
> [ 1151.420923] LATENCY reclaim= 43 migrate=128 migrateranges=23
> [ 1151.421209] LATENCY reclaim= 11 migrate=253 migrateranges=14
> [ 1151.427856] LATENCY reclaim= 45 migrate=12 migrateranges=12
> [ 1151.434485] LATENCY reclaim= 44 migrate=33 migrateranges=12
> [ 1151.440975] LATENCY reclaim= 45 migrate=0 migrateranges=11
> [ 1151.447513] LATENCY reclaim= 39 migrate=35 migrateranges=11
> [ 1151.453919] LATENCY reclaim= 46 migrate=0 migrateranges=12
> [ 1151.460474] LATENCY reclaim= 39 migrate=41 migrateranges=11
> [ 1151.466947] LATENCY reclaim= 54 migrate=32 migrateranges=17
> [ 1151.473464] LATENCY reclaim= 45 migrate=21 migrateranges=12
> [ 1151.480016] LATENCY reclaim= 41 migrate=39 migrateranges=12
> [ 1151.486551] LATENCY reclaim= 41 migrate=36 migrateranges=12
> [ 1151.493199] LATENCY reclaim= 13 migrate=188 migrateranges=12
> [ 1151.500034] LATENCY reclaim= 60 migrate=94 migrateranges=13
> [ 1151.506686] LATENCY reclaim= 78 migrate=9 migrateranges=12
> [ 1151.513313] LATENCY reclaim= 33 migrate=147 migrateranges=12
> [ 1151.519839] LATENCY reclaim= 52 migrate=98 migrateranges=12
> [ 1151.526556] LATENCY reclaim= 46 migrate=126 migrateranges=12
> [ 1151.533254] LATENCY reclaim= 22 migrate=230 migrateranges=12
> [ 1151.540145] LATENCY reclaim= 0 migrate=305 migrateranges=13
> [ 1151.546997] LATENCY reclaim= 1 migrate=301 migrateranges=13
> [ 1151.553686] LATENCY reclaim= 40 migrate=201 migrateranges=12
> [ 1151.560395] LATENCY reclaim= 35 migrate=149 migrateranges=12
> [ 1151.567076] LATENCY reclaim= 77 migrate=43 migrateranges=16
> [ 1151.573836] LATENCY reclaim= 34 migrate=190 migrateranges=12
> [ 1151.580510] LATENCY reclaim= 51 migrate=120 migrateranges=12
> [ 1151.587240] LATENCY reclaim= 33 migrate=147 migrateranges=13
> [ 1151.594036] LATENCY reclaim= 20 migrate=241 migrateranges=13
> [ 1151.600749] LATENCY reclaim= 75 migrate=41 migrateranges=13
> [ 1151.607402] LATENCY reclaim= 77 migrate=32 migrateranges=12
> [ 1151.613956] LATENCY reclaim= 72 migrate=35 migrateranges=12
> [ 1151.620642] LATENCY reclaim= 59 migrate=162 migrateranges=12
> [ 1151.627181] LATENCY reclaim= 76 migrate=9 migrateranges=11
> [ 1151.633795] LATENCY reclaim= 80 migrate=0 migrateranges=12
> [ 1151.640278] LATENCY reclaim= 87 migrate=18 migrateranges=12
> [ 1151.646758] LATENCY reclaim= 82 migrate=10 migrateranges=11
> [ 1151.653307] LATENCY reclaim= 71 migrate=31 migrateranges=12
> [ 1151.659911] LATENCY reclaim= 61 migrate=77 migrateranges=12
> [ 1151.666514] LATENCY reclaim= 94 migrate=42 migrateranges=15
> [ 1151.673089] LATENCY reclaim= 67 migrate=59 migrateranges=12
> [ 1151.679655] LATENCY reclaim= 81 migrate=14 migrateranges=12
> [ 1151.686253] LATENCY reclaim= 49 migrate=93 migrateranges=12
> [ 1151.692815] LATENCY reclaim= 61 migrate=54 migrateranges=12
> [ 1151.699438] LATENCY reclaim= 42 migrate=99 migrateranges=10
> [ 1151.705881] OVERALL overall=285157

cumulative numbers are

reclaim:2222 migrate:3995 migrateranges:552 sum:6217

So those code paths you were measuring were contributing to the overal
latency only marginally (~2%).
 
> cma_alloc latency is = 297385 us

As I've said earlier I would just use perf with the call graph support
and look at the time distribution to see where the bottleneck is.
-- 
Michal Hocko
SUSE Labs