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

[Nick Piggin]

Andrew Morton wrote:
> Christoph Lameter <clameter@xxxxxxx> 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.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/