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Date: Thu, 12 Jul 2001 11:26:13 +0200
From: Andi Kleen <ak@suse.de>
To: lvm-devel@sistina.com
Cc: Lance Larsh <llarsh@oracle.com>,
        Brian Strand <bstrand@switchmanagement.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [lvm-devel] Re: 2x Oracle slowdown from 2.2.16 to 2.4.4
Message-ID: <20010712112613.A14134@gruyere.muc.suse.de>
In-Reply-To: <3B4C8263.6000407@switchmanagement.com> <Pine.LNX.4.21.0107111530170.2342-100000@llarsh-pc3.us.oracle.com> <20010712043046.R3496@athlon.random>
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In-Reply-To: <20010712043046.R3496@athlon.random>; from andrea@suse.de on Thu, Jul 12, 2001 at 04:30:46AM +0200
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On Thu, Jul 12, 2001 at 04:30:46AM +0200, Andrea Arcangeli wrote:
> I will soon somehow make those changes in the lvm (based on beta7) in my
> tree and it will be interesting to see if this will make a difference. I
> will also have a look to see if I can improve a little more the lvm_map
> but other than those non rw semaphores there should be not a significant
> overhead to remove in the lvm fast path.

Even if you fix the snapshot_sem you still have the down on the _pe_lock 
in lvm_map. The part covered by the PE lock is only a few tenths of cycles
shorter than the part covered by the snapshot semaphore; so it is unlikely
that you see much difference unless you change both to rwsems.

Wouldn't a single semaphore be enough BTW to cover both? 


-Andi



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