From: Thomas Gleixner <tglx@linutronix.de>
To: George Spelvin <linux@horizon.com>
Cc: eric.dumazet@gmail.com, linux-kernel@vger.kernel.org,
riel@redhat.com, torvalds@linux-foundation.org
Subject: Re: [patch 2/7] lib/hashmod: Add modulo based hash mechanism
Date: Sun, 1 May 2016 10:35:54 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.11.1605011012020.3692@nanos> (raw)
In-Reply-To: <20160430205235.24232.qmail@ns.horizon.com>
On Sat, 30 Apr 2016, George Spelvin wrote:
> Thomas Gleixner wrote:
> You say that
> > hash64 is slightly faster as the modulo prime as it does not have the
> > multiplication.
>
> Um... are you sure you benchmarked that right? The hash_64 code you
> used (Thomas Wang's 64->32-bit hash) has a critical path consisting of 6
> shifts and 7 adds. I can't believe that's faster than a single multiply.
Sorry I did not express myself clear enough.
hash64 (the single multiply with the adjusted golden ratio) is slightly faster
than the modulo one which has two mutiplications.
So here is the list:
hash_64(): (key * GOLDEN_RATIO) >> (64 - bits) 31Mio Ops/sec
modulo: 28Mio Ops/sec
Thomas Wangs 64 -> 32 bit 21Mio Ops/sec
Thanks,
tglx
next prev parent reply other threads:[~2016-05-01 8:37 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CA+55aFxBWfAHQNAdBbdVr+z8ror4GVteyce3D3=vwDWxhu5KqQ@mail.gmail.com>
2016-04-30 20:52 ` [patch 2/7] lib/hashmod: Add modulo based hash mechanism George Spelvin
2016-05-01 8:35 ` Thomas Gleixner [this message]
2016-05-01 9:43 ` George Spelvin
2016-05-01 16:51 ` Linus Torvalds
2016-05-14 3:54 ` George Spelvin
2016-05-14 18:35 ` Linus Torvalds
2016-05-02 7:11 ` Thomas Gleixner
2016-05-02 10:20 ` [PATCH 1/2] <linux/hash.h>: Make hash_64(), hash_ptr() return 32 bits George Spelvin
2016-05-02 10:22 ` [PATCH 2/2] <linux/hash.h>: Fix hash_64()'s horrible collision problem George Spelvin
2016-05-02 20:08 ` Linus Torvalds
2016-05-02 10:27 ` [RFC PATCH 3/2] (Rant) Fix various hash abuses George Spelvin
2016-05-02 10:31 ` [RFC PATCH 4/2] namei: Improve hash mixing if CONFIG_DCACHE_WORD_ACCESS George Spelvin
2016-05-16 18:51 ` Linus Torvalds
2016-05-02 13:28 ` [PATCH 1/2] <linux/hash.h>: Make hash_64(), hash_ptr() return 32 bits Peter Zijlstra
2016-05-02 19:08 ` George Spelvin
2016-05-02 16:24 ` Linus Torvalds
2016-05-02 20:26 ` George Spelvin
2016-05-02 21:19 ` Linus Torvalds
2016-05-02 21:41 ` Linus Torvalds
2016-05-03 1:59 ` George Spelvin
2016-05-03 3:01 ` Linus Torvalds
2016-04-29 2:57 [patch 2/7] lib/hashmod: Add modulo based hash mechanism George Spelvin
2016-04-29 3:16 ` Linus Torvalds
2016-04-29 4:12 ` George Spelvin
2016-04-29 23:31 ` George Spelvin
2016-04-30 0:05 ` Linus Torvalds
2016-04-30 0:32 ` George Spelvin
2016-04-30 1:12 ` Linus Torvalds
2016-04-30 3:04 ` George Spelvin
-- strict thread matches above, loose matches on Subject: below --
2016-04-28 16:42 [patch 0/7] futex: Add support for process private hashing Thomas Gleixner
2016-04-28 16:42 ` [patch 2/7] lib/hashmod: Add modulo based hash mechanism Thomas Gleixner
2016-04-28 18:32 ` Linus Torvalds
2016-04-28 23:26 ` Thomas Gleixner
2016-04-29 2:25 ` Linus Torvalds
2016-04-30 13:02 ` Thomas Gleixner
2016-04-30 16:45 ` Eric Dumazet
2016-04-30 17:12 ` Linus Torvalds
2016-04-30 17:37 ` Eric Dumazet
2016-06-12 12:18 ` Sandy Harris
2016-04-29 21:10 ` Linus Torvalds
2016-04-29 23:51 ` Linus Torvalds
2016-04-30 1:34 ` Rik van Riel
2016-05-02 9:39 ` Torvald Riegel
2016-04-30 15:22 ` Thomas Gleixner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=alpine.DEB.2.11.1605011012020.3692@nanos \
--to=tglx@linutronix.de \
--cc=eric.dumazet@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@horizon.com \
--cc=riel@redhat.com \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox