linux-kernel - Re: [PATCH v1 2/2] zram: remove init_lock in zram_make

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Date:	Thu, 29 Jan 2015 15:06:04 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, Nitin Gupta <ngupta@...are.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Ganesh Mahendran <opensource.ganesh@...il.com>
Subject: Re: [PATCH v1 2/2] zram: remove init_lock in zram_make_request

On (01/29/15 14:28), Minchan Kim wrote:
> > I'm still concerned about performance numbers that I see on my x86_64.
> > it's not always, but mostly slower. I'll give it another try (disable
> > lockdep, etc.), but if we lose 10% on average then, sorry, I'm not so
> > positive about srcu change and will tend to vote for your initial commit
> > that simply moved meta free() out of init_lock and left locking as is
> > (lockdep warning would have been helpful there, because otherwise it
> > just looked like we change code w/o any reason).
> > 
> > what do you thunk?
> 
> Surely I agreee with you. If it suffers from 10% performance regression,
> it's absolutely no go.
> 
> However, I believe it should be no loss because that's one of the reason
> from RCU birth which should be really win in read-side lock path compared
> to other locking.
> 
> Please test it with dd or something for block-based test for removing
> noise from FS. I also will test it to confirm that with real machine.
> 

do you test with a single dd thread/process?  just dd if=foo of=bar -c... or
you start N `dd &' processes?

for a single writer there should be no difference, no doubt. I'm more
interested in multi-writer/multi-reader/mixed use cases.

the options that I use are: iozone -t 3 -R -r 16K -s 60M -I +Z
and -I is:
	-I  Use VxFS VX_DIRECT, O_DIRECT,or O_DIRECTIO for all file operations

with O_DIRECT I don't think there is a lot of noise, but I'll try to use
different benchmarks a bit later.


	-ss
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