linux-kernel - Re: [PATCH] fs/proc: Move kfree outside pde_unload

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Message-ID: <5037AFB9.5010001@sgi.com>
Date:	Fri, 24 Aug 2012 11:45:45 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<adobriyan@...il.com>, Alexander Viro <viro@...iv.linux.org.uk>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] fs/proc: Move kfree outside pde_unload_lock

On 08/24/2012 09:58 AM, Eric Dumazet wrote:
> Le vendredi 24 août 2012 à 09:48 -0500, Nathan Zimmer a écrit :
>> On Wed, Aug 22, 2012 at 11:42:58PM +0200, Eric Dumazet wrote:
>>> On Wed, 2012-08-22 at 20:28 +0200, Eric Dumazet wrote:
>>>
>>>> Thats interesting, but if you really want this to fly, one RCU
>>>> conversion would be much better ;)
>>>>
>>>> pde_users would be an atomic_t and you would avoid the spinlock
>>>> contention.
>>> Here is what I had in mind, I would be interested to know how it helps a 512 core machine ;)
>>>
>> Here are the results and they look great.
>>
>> cpuinfo	baseline	moved kfree	Rcu
>> tasks	read-sec	read-sec	read-sec
>> 1	0.0141		0.0141		0.0141
>> 2	0.0140		0.0140		0.0142
>> 4	0.0140		0.0141		0.0141
>> 8	0.0145		0.0145		0.0140
>> 16	0.0553		0.0548		0.0168
>> 32	0.1688		0.1622		0.0549
>> 64	0.5017		0.3856		0.1690
>> 128	1.7005		0.9710		0.5038
>> 256	5.2513		2.6519		2.0804
>> 512	8.0529		6.2976		3.0162
>>
>>
>>
> Indeed...
>
> Could you explicit the test you are actually doing ?
>
> Thanks
>
>


It is a dead simple test.
The test starts by forking off X number of tasks
assigning each their own cpu.
Each task then allocs a bit of memory.
All tasks wait on a memory cell for the go order.
We measure the read time starting here.
Once the go order is given they all read a chunk of the selected proc file.
I was using /proc/cpuinfo to test.
Once everyone has finished we take the end read time.




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