On 11/07/2017 12:05, Stefan Hajnoczi wrote: > On Mon, Jul 10, 2017 at 05:08:56PM +0200, Paolo Bonzini wrote: >> On 10/07/2017 17:07, Stefan Hajnoczi wrote: >>> On Wed, Jul 05, 2017 at 09:36:32PM +0800, Fam Zheng wrote: >>>> Allow block driver to map and unmap a buffer for later I/O, as a >>>> performance >>>> hint. >>> The name blk_dma_map() is confusing since other "dma" APIs like >>> dma_addr_t and dma_blk_io() deal with guest physical addresses instead >>> of host addresses. They are about DMA to/from guest RAM. >>> >>> Have you considered hiding this cached mapping in block/nvme.c so that >>> it isn't exposed? block/nvme.c could keep the last buffer mapped and >>> callers would get the performance benefit without a new blk_dma_map() >>> API. >> >> One buffer is enough for qemu-img bench, but not for more complex cases >> (e.g. fio). > > I don't see any other blk_dma_map() callers.
Indeed, the fio plugin is not part of this series, but it also used blk_dma_map. Without it, performance is awful. Paolo
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