Am 10.03.2017 um 11:02 schrieb Wei Wang: > On 03/08/2017 12:01 PM, Michael S. Tsirkin wrote: >> On Fri, Mar 03, 2017 at 01:40:28PM +0800, Wei Wang wrote: >>> From: Liang Li <liang.z.li@xxxxxxxxx> >>> >>> The implementation of the current virtio-balloon is not very >>> efficient, because the pages are transferred to the host one by one. >>> Here is the breakdown of the time in percentage spent on each >>> step of the balloon inflating process (inflating 7GB of an 8GB >>> idle guest). >>> >>> 1) allocating pages (6.5%) >>> 2) sending PFNs to host (68.3%) >>> 3) address translation (6.1%) >>> 4) madvise (19%) >>> >>> It takes about 4126ms for the inflating process to complete. >>> The above profiling shows that the bottlenecks are stage 2) >>> and stage 4). >>> >>> This patch optimizes step 2) by transfering pages to the host in >>> chunks. A chunk consists of guest physically continuous pages, and >>> it is offered to the host via a base PFN (i.e. the start PFN of >>> those physically continuous pages) and the size (i.e. the total >>> number of the pages). A normal chunk is formated as below: >>> ----------------------------------------------- >>> | Base (52 bit) | Size (12 bit)| >>> ----------------------------------------------- >>> For large size chunks, an extended chunk format is used: >>> ----------------------------------------------- >>> | Base (64 bit) | >>> ----------------------------------------------- >>> ----------------------------------------------- >>> | Size (64 bit) | >>> ----------------------------------------------- >>> >>> By doing so, step 4) can also be optimized by doing address >>> translation and madvise() in chunks rather than page by page. >>> >>> This optimization requires the negotation of a new feature bit, >>> VIRTIO_BALLOON_F_CHUNK_TRANSFER. >>> >>> With this new feature, the above ballooning process takes ~590ms >>> resulting in an improvement of ~85%. >>> >>> TODO: optimize stage 1) by allocating/freeing a chunk of pages >>> instead of a single page each time. >>> >>> Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx> >>> Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx> >>> Suggested-by: Michael S. Tsirkin <mst@xxxxxxxxxx> >>> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx> >>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> >>> Cc: Cornelia Huck <cornelia.huck@xxxxxxxxxx> >>> Cc: Amit Shah <amit.shah@xxxxxxxxxx> >>> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> >>> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> >>> Cc: David Hildenbrand <david@xxxxxxxxxx> >>> Cc: Liang Li <liliang324@xxxxxxxxx> >>> Cc: Wei Wang <wei.w.wang@xxxxxxxxx> >> Does this pass sparse? I see some endian-ness issues here. > > "pass sparse"- what does that mean? > I didn't see any complaints from "make" on my machine. https://kernel.org/doc/html/latest/dev-tools/sparse.html Static code analysis. You have to run it explicitly. -- Thanks, David
