lkml.org 
[lkml]   [2009]   [Apr]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Fix dirty page accounting in redirty_page_for_writepage()
On Thu, 30 Apr 2009, Ingo Molnar wrote:

> > may not care too much about a event counter missing a beat once in
> > a while for platforms not supporting atomic per cpu ops. I know
> > this affects IA64. The cost of an atomic operations for an event
> > counter update (which would have avoided the potential of a
> > concurrent update) was not justifiable.
>
> when you say "atomics", do you mean the classic meaning of atomics?
> Because there are no classic atomics involved. This is the
> before/after disassembly from Eric's commit 4e69489a0:

The fallback for IA64 would be to use full (classic) atomic operations
(fetchadd) instead of fast atomic vs. interrupt as available on x86

> c0436275: 64 83 05 20 5f 6a c0 addl $0x1,%fs:0xc06a5f20
>
> There's no atomic instructions at all - the counters here are only
> accessed locally. They are local-irq-atomic, but not
> cacheline-atomic.

Right but that is not available on IA64. So one must choose between
manually disabling interrupts and then increment the counter (long code
sequence) and a classic atomic operation for the fallback.


\
 
 \ /
  Last update: 2009-04-30 18:23    [from the cache]
©2003-2011 Jasper Spaans