> On Wednesday 14 October 2009 17:48:39 ext epsi@xxxxxx wrote: > > Mem clock is both times 166MHz. I don't know whether are differences in > > cycle access and timing, but memclock is fine. > > > > Following Siarhei hints of initialize the buffers (around 1.2 MByte > each) > > I get different results in 22kernel for use of > > malloc alone > > memcpy = 473.764, loop4 = 448.430, loop1 = 102.770, rand = > 29.641 > > calloc alone > > memcpy = 405.947, loop4 = 361.550, loop1 = 95.441, rand = > 21.853 > > malloc+memset: > > memcpy = 239.294, loop4 = 188.617, loop1 = 80.871, rand = > 4.726 > > > > In 31kernel all 3 measures are about the same (unfortunatly low) level > of > > malloc+memset in 22. > > > > First of all: What performance can be expected? > > Does 22 make failures if it is so much faster? > > Can the later kernels get a boost in memory handling? > > What you see is just a (fake) performance boost because you have a single > physical page shared between all the virtual pages in the source buffer. > So > you get no cache misses on read operations and everything seems fast. > > This is unlikely to happen on real use, and it does not reflect real > memory > performance. So the benchmark is inadequate. > > You can get some basic information here: > http://en.wikipedia.org/wiki/Copy-on-write > > Regarding the difference in behavior between .22 and recent kernels. It > may be > some regression in copy-on-write implementation, or just some change done > on > purpose. That is assuming that the userspace stuff was identical in both > tests. > Ok, understand the difference if the memory is uninitialised. But why there is the difference in "malloc + memset" and "calloc"? In both cases the memory will be cleared. -- Jetzt kostenlos herunterladen: Internet Explorer 8 und Mozilla Firefox 3.5 - sicherer, schneller und einfacher! http://portal.gmx.net/de/go/atbrowser -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
