linux-kernel - Re: [PATCH v1 5/9] perf util: Remove a set of shadow stats static variables

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 21 Nov 2017 22:19:50 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Jin Yao <yao.jin@...ux.intel.com>, acme@...nel.org,
        jolsa@...nel.org, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v1 5/9] perf util: Remove a set of shadow stats static
 variables

On Tue, Nov 21, 2017 at 10:03:50AM -0800, Andi Kleen wrote:
> > all this is about switching from array to rb_list for the --per-thread case,
> > which can be considered as a special use case.. how much do we suffer in
> > performance with new code? how about the "perf stat -I 100", would it scale
> > ok for extreme cases (many events in -e or -dddd..)
> 
> rbtrees scale by log N, with N being the entries in the tree.
> 
> Even in extreme cases, let's say 10000 events and 1000 cpus it would
> need only 8 memory accesses and comparisons for each look up.
> Even if we assume cache misses for all of the memory lookups,
> at ~200ns per cache miss it's still only 1us per event, which 
> is negligible.
> 
> In practice not all memory accesses will be misses because
> the upper levels of the tree are almost certainly cached
> from earlier accesses.

sounds good, thanks

jirka