Il 05/04/2013 21:23, Kevin Wolf ha scritto: >> > virtually all dup pages are zero pages. remove >> > the special is_dup_page() function and use the >> > optimized buffer_find_nonzero_offset() function >> > instead. >> > >> > here buffer_find_nonzero_offset() is used directly >> > to avoid the unnecssary additional checks in >> > buffer_is_zero(). >> > >> > raw performace gain checking 1 GByte zeroed memory >> > over is_dup_page() is approx. 10-12% with SSE2 >> > and 8-10% with unsigned long arithmedtic. >> > >> > Signed-off-by: Peter Lieven <p...@kamp.de> >> > Reviewed-by: Orit Wasserman <owass...@redhat.com> >> > Reviewed-by: Eric Blake <ebl...@redhat.com> > Okay, so I bisected again and this is the second patch that is involved > in the slowness of qemu-iotests case 007. > > The problem seems to be that the RAM of a guest is in fact _not_ zeroed > during initialisation. It hits my test case reliably because I'm running > with MALLOC_PERTURB_. Now I'm wondering if in practice this happens only > under such test conditions, or if real guests could be affected as well > and we should make sure to get zeroed memory for RAM.
I think we should MADV_DONTNEED it. Paolo
