From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
kernel test robot <rong.a.chen@intel.com>,
Jann Horn <jannh@google.com>, LKML <linux-kernel@vger.kernel.org>,
x86-ml <x86@kernel.org>, Ingo Molnar <mingo@kernel.org>,
Borislav Petkov <bp@suse.de>,
lkp@lists.01.org
Subject: Re: [futex] 8019ad13ef: will-it-scale.per_process_ops -97.8% regression
Date: Mon, 09 Mar 2020 10:34:48 +0100 [thread overview]
Message-ID: <87y2s97txj.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20200309085123.GE12561@hirez.programming.kicks-ass.net>
Peter Zijlstra <peterz@infradead.org> writes:
> On Sun, Mar 08, 2020 at 07:07:17PM +0100, Thomas Gleixner wrote:
>> static struct futex_hash_bucket *hash_futex(union futex_key *key)
>> {
>> - u32 hash = jhash2((u32*)&key->both.word,
>> - (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
>> + u32 hash = jhash2((u32*)&key->both.ptr,
>> + (sizeof(key->both.ptr) + sizeof(key->both.word)) / 4,
>> key->both.offset);
>> return &futex_queues[hash & (futex_hashsize - 1)];
>> }
>
> Groan... I've gotta ask, why isn't that written like:
>
> u32 hash = jhash2((u32 *)key,
> offsetof(typeof(*key), offset) / 4
> key->both.offset);
>
> Or better yet:
>
> u32 hash = jhash((u32 *)key, sizeof(*key) / 4, 0);
Histerical raisins :)
next prev parent reply other threads:[~2020-03-09 9:35 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-08 14:02 [futex] 8019ad13ef: will-it-scale.per_process_ops -97.8% regression kernel test robot
[not found] ` <CAHk-=wgJV7xrxsTkOG203huPShzZBEC6N_BG0KGwHBmEq4yqWg@mail.gmail.com>
2020-03-08 15:28 ` Linus Torvalds
2020-03-08 18:07 ` Thomas Gleixner
2020-03-09 8:26 ` kernel test robot
2020-03-09 8:51 ` Peter Zijlstra
2020-03-09 9:34 ` Thomas Gleixner [this message]
2020-03-09 21:42 ` [tip: locking/urgent] futex: Unbreak futex hashing tip-bot2 for Thomas Gleixner
2020-03-11 8:20 ` [futex] 8019ad13ef: will-it-scale.per_process_ops -97.8% regression Thierry Reding
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