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

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Date:	Fri, 24 Aug 2012 16:43:31 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	Nathan Zimmer <nzimmer@....com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	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 Fri, Aug 24, 2012 at 11:45:45AM -0500, Nathan Zimmer wrote:
> 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.
>

Here is the text for those who are curious.


View attachment "readproc.c" of type "text/x-c++src" (4391 bytes)