Re: page table lock patch V15 [0/7]: overview

From: Nick Piggin <nickpiggin_at_yahoo.com.au>
Date: 2005-01-13 10:16:54
Andrew Morton wrote:
> Christoph Lameter <clameter@sgi.com> wrote:
> 
>>>Do we have measurements of the negative and/or positive impact on smaller
>>
>> > machines?
>>
>> Here is a measurement of 256M allocation on a 2 way SMP machine 2x
>> PIII-500Mhz:
>>
>>  Gb Rep Threads   User      System     Wall flt/cpu/s fault/wsec
>>   0  10    1    0.005s      0.016s   0.002s 54357.280  52261.895
>>   0  10    2    0.008s      0.019s   0.002s 43112.368  42463.566
>>
>> With patch:
>>
>>  Gb Rep Threads   User      System     Wall flt/cpu/s fault/wsec
>>   0  10    1    0.005s      0.016s   0.002s 54357.280  53439.357
>>   0  10    2    0.008s      0.018s   0.002s 44650.831  44202.412
>>
>> So only a very minor improvements for old machines (this one from ~ 98).
> 
> 
> OK.  But have you written a test to demonstrate any performance
> regressions?  From, say, the use of atomic ops on ptes?
> 

Performance wise, Christoph's never had as much of a problem as my
patches because it isn't doing extra atomic operations in copy_page_range.

However, it looks like it should be. For the same reason there needs to
be an atomic read in handle_mm_fault. And it probably needs atomic ops
in other places too, I think.

So my patches cost about 7% in lmbench fork benchmark... however, I've
been thinking we could take the mmap_sem for writing before doing the
copy_page_range which could reduce the need for atomic ops.


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Received on Wed Jan 12 18:23:31 2005

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