Commit 3edcd7e6 authored by Peter Lieven's avatar Peter Lieven Committed by Juan Quintela
Browse files

migration: search for zero instead of dup pages 



virtually all dup pages are zero pages. remove
the special is_dup_page() function and use the
optimized buffer_find_nonzero_offset() function
instead.

here buffer_find_nonzero_offset() is used directly
to avoid the unnecssary additional checks in
buffer_is_zero().

raw performace gain checking 1 GByte zeroed memory
over is_dup_page() is approx. 10-12% with SSE2
and 8-10% with unsigned long arithmedtic.

Signed-off-by: default avatarPeter Lieven <pl@kamp.de>
Reviewed-by: default avatarOrit Wasserman <owasserm@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Signed-off-by: default avatarJuan Quintela <quintela@redhat.com>
parent 49f676a0

arch_init.c

+6 −15
Original line number Diff line number Diff line
@@ -146,19 +146,10 @@ int qemu_read_default_config_files(bool userconfig) 
    return 0;

}



static int is_dup_page(uint8_t *page)

static inline bool is_zero_page(uint8_t *p)

{

    VECTYPE *p = (VECTYPE *)page;

    VECTYPE val = SPLAT(page);

    int i;



    for (i = 0; i < TARGET_PAGE_SIZE / sizeof(VECTYPE); i++) {

        if (!ALL_EQ(val, p[i])) {

            return 0;

        }

    }



    return 1;

    return buffer_find_nonzero_offset(p, TARGET_PAGE_SIZE) ==

        TARGET_PAGE_SIZE;

}



/* struct contains XBZRLE cache and a static page
@@ -445,12 +436,12 @@ static int ram_save_block(QEMUFile *f, bool last_stage) 


            /* In doubt sent page as normal */

            bytes_sent = -1;

            if (is_dup_page(p)) {

            if (is_zero_page(p)) {

                acct_info.dup_pages++;

                bytes_sent = save_block_hdr(f, block, offset, cont,

                                            RAM_SAVE_FLAG_COMPRESS);

                qemu_put_byte(f, *p);

                bytes_sent += 1;

                qemu_put_byte(f, 0);

                bytes_sent++;

            } else if (migrate_use_xbzrle()) {

                current_addr = block->offset + offset;

                bytes_sent = save_xbzrle_page(f, p, current_addr, block,