| Message ID | 513F4F1E.2060400@dlhnet.de |
|---|---|
| State | New |
| Headers | show |
On 03/12/2013 09:51 AM, Peter Lieven wrote: > at the beginning of migration all pages are marked dirty and > in the first round a bulk migration of all pages is performed. > > currently all these pages are copied to the page cache regardless > if there are frequently updated or not. this doesn't make sense > since most of these pages are never transferred again. > > this patch changes the XBZRLE transfer to only be used after > the bulk stage has been completed. that means a page is added > to the page cache the second time it is transferred and XBZRLE > can benefit from the third time of transfer. > > since the page cache is likely smaller than the number of pages > its also likely that in the second round the page is missing in the > cache due to collisions in the bulk phase. > > on the other hand a lot of unneccssary mallocs, memdups and frees s/unneccssary/unnecessary/ > are saved. Earlier, I asked you for some benchmark numbers, and you provided some. Mentioning them in the commit message will make an even stronger argument for including this patch.
diff --git a/arch_init.c b/arch_init.c index 3d09327..04c82e4 100644 --- a/arch_init.c +++ b/arch_init.c @@ -451,7 +451,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage) RAM_SAVE_FLAG_COMPRESS); qemu_put_byte(f, *p); bytes_sent += 1; - } else if (migrate_use_xbzrle()) { + } else if (!ram_bulk_stage && migrate_use_xbzrle()) { current_addr = block->offset + offset; bytes_sent = save_xbzrle_page(f, p, current_addr, block, offset, cont, last_stage);
at the beginning of migration all pages are marked dirty and in the first round a bulk migration of all pages is performed. currently all these pages are copied to the page cache regardless if there are frequently updated or not. this doesn't make sense since most of these pages are never transferred again. this patch changes the XBZRLE transfer to only be used after the bulk stage has been completed. that means a page is added to the page cache the second time it is transferred and XBZRLE can benefit from the third time of transfer. since the page cache is likely smaller than the number of pages its also likely that in the second round the page is missing in the cache due to collisions in the bulk phase. on the other hand a lot of unneccssary mallocs, memdups and frees are saved. Signed-off-by: Peter Lieven <pl@kamp.de> --- arch_init.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)