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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 :)

WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de>
To: 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>

[-- Attachment #1: Type: text/plain, Size: 772 bytes --]

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 :)

  reply	other threads:[~2020-03-09  9:35 UTC|newest]

Thread overview: 16+ 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
2020-03-08 14:02 ` kernel test robot
2020-03-08 14:22 ` Linus Torvalds
2020-03-08 15:28   ` Linus Torvalds
2020-03-08 15:28     ` Linus Torvalds
2020-03-08 18:07     ` Thomas Gleixner
2020-03-08 18:07       ` Thomas Gleixner
2020-03-09  8:26       ` kernel test robot
2020-03-09  8:26         ` kernel test robot
2020-03-09  8:51       ` Peter Zijlstra
2020-03-09  8:51         ` Peter Zijlstra
2020-03-09  9:34         ` Thomas Gleixner [this message]
2020-03-09  9:34           ` Thomas Gleixner
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
2020-03-11  8:20         ` Thierry Reding

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