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Re: [Qemu-devel] [PATCH v1 1/2] scsi-disk: support reporting of rotation
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v1 1/2] scsi-disk: support reporting of rotation rate |
Date: |
Wed, 4 Oct 2017 17:49:44 +0100 |
User-agent: |
Mutt/1.9.0 (2017-09-02) |
* Daniel P. Berrange (address@hidden) wrote:
> The Linux kernel will query the SCSI "Block device characteristics"
> VPD to determine the rotations per minute of the disk. If this has
> the value 1, it is taken to be an SSD and so Linux sets the
> 'rotational' flag to 0 for the I/O queue and will stop using that
> disk as a source of random entropy. Other operating systems may
> also take into account rotation rate when setting up default
> behaviour.
>
> Mgmt apps should be able to set the rotation rate for virtualized
> block devices, based on characteristics of the host storage in use,
> so that the guest OS gets sensible behaviour out of the box. This
> patch thus adds a 'rotation-rate' parameter for 'scsi-hd' and
> 'scsi-block' device types. For the latter, this parameter will be
> ignored unless the host device has TYPE_DISK.
>
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
> hw/scsi/scsi-disk.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
> index 6e841fb5ff..a518080e7d 100644
> --- a/hw/scsi/scsi-disk.c
> +++ b/hw/scsi/scsi-disk.c
> @@ -104,6 +104,14 @@ typedef struct SCSIDiskState
> char *product;
> bool tray_open;
> bool tray_locked;
> + /*
> + * 0x0000 - rotation rate not reported
> + * 0x0001 - non-rotating medium (SSD)
> + * 0x0002-0x0400 - reserved
> + * 0x0401-0xffe - rotations per minute
> + * 0xffff - reserved
> + */
> + uint16_t rotation_rate;
> } SCSIDiskState;
>
> static bool scsi_handle_rw_error(SCSIDiskReq *r, int error, bool
> acct_failed);
> @@ -605,6 +613,7 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req,
> uint8_t *outbuf)
> outbuf[buflen++] = 0x83; // device identification
> if (s->qdev.type == TYPE_DISK) {
> outbuf[buflen++] = 0xb0; // block limits
> + outbuf[buflen++] = 0xb1; /* block device characteristics */
> outbuf[buflen++] = 0xb2; // thin provisioning
> }
> break;
> @@ -747,6 +756,15 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req,
> uint8_t *outbuf)
> outbuf[43] = max_io_sectors & 0xff;
> break;
> }
> + case 0xb1: /* block device characteristics */
> + {
> + buflen = 8;
> + outbuf[4] = (s->rotation_rate >> 8) & 0xff;
> + outbuf[5] = s->rotation_rate & 0xff;
> + outbuf[6] = 0;
> + outbuf[7] = 0;
> + break;
> + }
> case 0xb2: /* thin provisioning */
> {
> buflen = 8;
> @@ -2911,6 +2929,7 @@ static Property scsi_hd_properties[] = {
> DEFAULT_MAX_UNMAP_SIZE),
> DEFINE_PROP_UINT64("max_io_size", SCSIDiskState, max_io_size,
> DEFAULT_MAX_IO_SIZE),
> + DEFINE_PROP_UINT16("rotation_rate", SCSIDiskState, rotation_rate, 0),
> DEFINE_BLOCK_CHS_PROPERTIES(SCSIDiskState, qdev.conf),
> DEFINE_PROP_END_OF_LIST(),
> };
> @@ -2982,6 +3001,7 @@ static const TypeInfo scsi_cd_info = {
> static Property scsi_block_properties[] = {
> DEFINE_BLOCK_ERROR_PROPERTIES(SCSIDiskState, qdev.conf), \
> DEFINE_PROP_DRIVE("drive", SCSIDiskState, qdev.conf.blk),
> + DEFINE_PROP_UINT16("rotation_rate", SCSIDiskState, rotation_rate, 0),
> DEFINE_PROP_END_OF_LIST(),
> };
Are you sure you want this as a property of SCSIDiskState etc rather
than a property on the underlying drive?
Then if virtio devices etc wanted to pick this up later they could
without needing extra parameters.
Dave
>
> --
> 2.13.5
>
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK