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From: Thomas Gleixner <tglx@linutronix.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Darren Hart <darren@dvhart.com>,
	Michael Kerrisk <mtk.manpages@googlemail.com>,
	Davidlohr Bueso <dave@stgolabs.net>, Chris Mason <clm@fb.com>,
	"Carlos O'Donell" <carlos@redhat.com>,
	Torvald Riegel <triegel@redhat.com>,
	Eric Dumazet <edumazet@google.com>
Subject: Re: [patch 2/7] lib/hashmod: Add modulo based hash mechanism
Date: Fri, 29 Apr 2016 01:26:14 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.11.1604290119320.3718@nanos> (raw)
In-Reply-To: <CA+55aFzMtEVc_5QS8EUvdKYfNMmJ9fpgcM4iEhdwaY1Oe=JYmw@mail.gmail.com>

On Thu, 28 Apr 2016, Linus Torvalds wrote:
> 
> I'd really hate to add *another* ad-hoc hash when the previous ad-hoc
> hash has been shown to be bad.

I completely agree.

I'm not a hashing wizard and I completely failed to understand why
hash_long/ptr are so horrible for the various test cases I ran.

So my ad hoc test was to use the only hash function I truly understand. It was
state of the art in my university days :) And surprise, surprise it worked
really well.

My main focus was really to solve this futex issue which plages various people
and not to dive into hashing theory for a few weeks.

I'll try to dig up some time to analyze the hash_long failure unless someone
familiar with the problem is beating me to it.

Thanks,

	tglx

  reply	other threads:[~2016-04-28 23:27 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-28 16:42 [patch 0/7] futex: Add support for process private hashing Thomas Gleixner
2016-04-28 16:42 ` [patch 1/7] futex: Add some more function commentry 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 [this message]
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
2016-04-28 16:42 ` [patch 3/7] futex: Hash private futexes per process Thomas Gleixner
2016-04-28 16:42 ` [patch 4/7] futex: Add op for hash preallocation Thomas Gleixner
2016-04-28 16:42 ` [patch 5/7] futex: Add sysctl knobs for process private hash Thomas Gleixner
2016-04-28 16:42 ` [patch 6/7] perf/bench/futex-hash: Support NUMA Thomas Gleixner
2016-04-28 16:42 ` [patch 7/7] perf/bench/futex-hash: Support preallocate hash table Thomas Gleixner
  -- strict thread matches above, loose matches on Subject: below --
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
     [not found] <CA+55aFxBWfAHQNAdBbdVr+z8ror4GVteyce3D3=vwDWxhu5KqQ@mail.gmail.com>
2016-04-30 20:52 ` George Spelvin
2016-05-01  8:35   ` Thomas Gleixner
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

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