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Wed, 6 Nov 2019 18:18:22 +0000 (UTC) Date: Wed, 6 Nov 2019 18:18:19 +0000 From: "Dr. David Alan Gilbert" To: Wei Yang Subject: Re: [PATCH 1/6] migration/postcopy: reduce memset when it is zero page and matches_target_page_size Message-ID: <20191106181819.GG2802@work-vm> References: <20191018004850.9888-1-richardw.yang@linux.intel.com> <20191018004850.9888-2-richardw.yang@linux.intel.com> MIME-Version: 1.0 In-Reply-To: <20191018004850.9888-2-richardw.yang@linux.intel.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-MC-Unique: 6CnZLKdHPwSZxpx4QvzNUQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Wei Yang (richardw.yang@linux.intel.com) wrote: > In this case, page_buffer content would not be used. >=20 > Skip this to save some time. >=20 > Signed-off-by: Wei Yang > --- > migration/ram.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) >=20 > diff --git a/migration/ram.c b/migration/ram.c > index 99a98b2da4..7938a643d9 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -4091,7 +4091,13 @@ static int ram_load_postcopy(QEMUFile *f) > switch (flags & ~RAM_SAVE_FLAG_CONTINUE) { > case RAM_SAVE_FLAG_ZERO: > ch =3D qemu_get_byte(f); > - memset(page_buffer, ch, TARGET_PAGE_SIZE); > + /* > + * Can skip to set page_buffer when > + * this is a zero page and (block->page_size =3D=3D TARGET_P= AGE_SIZE). > + */ When it's zero we will use place_page_zero which doesn't need to page_buffer; so yes that's OK; and you're right, the gotcha is with=20 mismatched page sizes where one subpage might be zero but not all of them; so yes it's right that we need that check. SO yes, Reviewed-by: Dr. David Alan Gilbert > + if (ch || !matches_target_page_size) { > + memset(page_buffer, ch, TARGET_PAGE_SIZE); > + } > if (ch) { > all_zero =3D false; > } > --=20 > 2.17.1 >=20 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK