Am 12.05.2014 08:09, schrieb Paolo Bonzini: > Il 10/05/2014 18:32, Peter Lieven ha scritto: >> What about XEN? >> > > You're right, Xen wouldn't work. Your original patch would not break it just > because Xen doesn't use migration (but the code would be broken). > > You would have to cache qemu_get_ram_block rather than qemu_get_ram_ptr, move > RAMBlock to memory-internal.h, and split the RAMBlock + ram_addr_t => void * > conversion out of qemu_get_ram_ptr and into a separate function (to be used > by memory_region_get_ram_ptr). > > I'm not sure of the benefit of your patch though. qemu_get_ram_block already > has a 1-item cache, are you seeing a low hit rate there? Or any other > profiling that shows qemu_get_ram_ptr as hot?
qemu_get_ram_ptr is hot only during migration. But the hit-rate of the LRU cache seems to be good. I am wondering if this is different if the migration has difficulties to converge, but you might be right it should be neglectible. I ran some basic migration tests with and without the patch. It might be that the results with the cache are slightly better, but the variance of the results is high. I had to run a significant number of tests to get more evidence. Peter > > Paolo
