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Re: [Qemu-devel] [PATCH v2 5/8] Use writev ops if available
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v2 5/8] Use writev ops if available |
Date: |
Thu, 21 Mar 2013 14:44:59 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
Il 21/03/2013 14:23, Orit Wasserman ha scritto:
> Update qemu_fflush and stdio_close to use writev ops if they are available
>
> Signed-off-by: Orit Wasserman <address@hidden>
> ---
> savevm.c | 30 ++++++++++++++++++++----------
> 1 file changed, 20 insertions(+), 10 deletions(-)
>
> diff --git a/savevm.c b/savevm.c
> index ab81dd3..fde59d3 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -292,7 +292,7 @@ static int stdio_fclose(void *opaque)
> QEMUFileStdio *s = opaque;
> int ret = 0;
>
> - if (s->file->ops->put_buffer) {
> + if (s->file->ops->put_buffer || s->file->ops->writev_buffer) {
> int fd = fileno(s->stdio_file);
> struct stat st;
>
> @@ -515,24 +515,34 @@ static void qemu_file_set_error(QEMUFile *f, int ret)
> }
> }
>
> -/** Flushes QEMUFile buffer
> +/**
> + * Flushes QEMUFile buffer
> *
> + * If there is writev_buffer QEMUFileOps it uses it otherwise uses
> + * put_buffer ops.
> */
> static void qemu_fflush(QEMUFile *f)
> {
> int ret = 0;
>
> - if (!f->ops->put_buffer) {
> + if (f->ops->writev_buffer) {
> + if (f->is_write && f->iovcnt > 0) {
> + ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt);
This needs to update f->pos.
> + }
> + } else if (f->ops->put_buffer) {
> + if (f->is_write && f->buf_index > 0) {
> + ret = f->ops->put_buffer(f->opaque, f->buf, f->pos,
> f->buf_index);
> + }
I think this has to go through all the iovecs (i.e. never look at
f->buf_index, only f->iovcnt). Otherwise RAM migration does not work,
because the page data is not copied to f->buf. But that's pretty much
it, the series looks good.
However, I'd still prefer to have qemu_put_buffer_no_copy coalesce
adjacent iovecs. Otherwise you might end up with only 3-400 bytes in
each sendmsg when serializing device data.
Paolo
> + } else {
> return;
> }
> - if (f->is_write && f->buf_index > 0) {
> - ret = f->ops->put_buffer(f->opaque, f->buf, f->pos, f->buf_index);
> - if (ret >= 0) {
> - f->pos += f->buf_index;
> - }
> - f->buf_index = 0;
> - f->iovcnt = 0;
> +
> + if (ret >= 0) {
> + f->pos += f->buf_index;
> }
> + f->buf_index = 0;
> + f->iovcnt = 0;
> +
> if (ret < 0) {
> qemu_file_set_error(f, ret);
> }
>
- [Qemu-devel] [PATCH v2 0/8] Migration: Remove copying of guest ram pages, Orit Wasserman, 2013/03/21
- [Qemu-devel] [PATCH v2 2/8] Add socket_writev_buffer function, Orit Wasserman, 2013/03/21
- [Qemu-devel] [PATCH v2 1/8] Add QemuFileWritevBuffer QemuFileOps, Orit Wasserman, 2013/03/21
- [Qemu-devel] [PATCH v2 3/8] Update bytes_xfer in qemu_put_byte, Orit Wasserman, 2013/03/21
- [Qemu-devel] [PATCH v2 6/8] More optimized qemu_put_be64/32/16, Orit Wasserman, 2013/03/21
- [Qemu-devel] [PATCH v2 4/8] Store the data to send also in iovec, Orit Wasserman, 2013/03/21
- [Qemu-devel] [PATCH v2 5/8] Use writev ops if available, Orit Wasserman, 2013/03/21
- Re: [Qemu-devel] [PATCH v2 5/8] Use writev ops if available,
Paolo Bonzini <=
- [Qemu-devel] [PATCH v2 7/8] Add qemu_put_buffer_no_copy, Orit Wasserman, 2013/03/21
- [Qemu-devel] [PATCH v2 8/8] Use qemu_put_buffer_no_copy for guest memory pages, Orit Wasserman, 2013/03/21