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migration: search for zero instead of dup pages

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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: Peter Lieven <pl@kamp.de>
Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
Peter Lieven 2013-03-26 10:58:35 +01:00 committed by Juan Quintela
parent 49f676a00a
commit 3edcd7e6eb
1 changed files with 6 additions and 15 deletions
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21
arch_init.c
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@ -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,