flush cache range proposal (was Re: ide errors in 7-rc1-mm1 and later)

Jeff Garzik
2004-06-10T17:51:07Z

Eric D. Mudama wrote:
> On Thu, Jun 10 at 8:11, Jens Axboe wrote:
>
>> On Thu, Jun 10 2004, Bartlomiej Zolnierkiewicz wrote:
>>
>>>
>>> /me just thinks loudly
>>>
>>> 'linear range' FLUSH CACHE seems so easy to implement that I always
>>> wondered
>>> why FLUSH CACHE command doesn't make any use of LBA address and number
>>> of sectors.
>>
>>
>> Indeed, that would be very helpful as well.
>
>
> Neat idea... so you send us a LBA and a block count, and we return
> good status if that region is flushed.
>
> Each command can specify a 32MiB region, assuming a device with
> 512-byte LBAs.
>
> Propose an exact implementation and an opcode...

Ok, I'll give it a shot:

1) IDENTIFY DEVICE, Word 206, Command set/feature supported

bit 15: shall be cleared to zero
bit 14: shall be set to one
bits 13:1: reserved
bits 0: 1 == flush cache (range) supported

Word 206:

If bit 0 is set to one, the mandatory FLUSH CACHE and FLUSH CACHE EXT
commands (if implemented) support the RANGE bit, and user-supplied LBA
and sector count specifying the limits of the cache flush. This bit
merely identifies the presence of this feature. Use word 207, bit 0, to
determine if the feature is enabled.

2) IDENTIFY DEVICE, Word 207, Command set/feature enabled

bit 15: shall be cleared to zero
bit 14: shall be set to one
bits 13:1: reserved
bits 0: 1 == flush cache (range) enabled

Word 206:

If bit 0 is set to one, the mandatory FLUSH CACHE and FLUSH CACHE EXT
commands (if implemented) support the RANGE bit, and user-supplied LBA
and sector count specifying the limits of the cache flush.

3) Modify FLUSH CACHE (E7h) as follows:

Inputs:
-------

Features: bit 0 (RANGE)
Sector Count: sector count
LBA Low: LBA(7:0)
LBA Mid: LBA(15:8)
LBA High: LBA(23:16)

Features -
If the RANGE bit is set, the cache flush operation shall be considered
to be limited to the region specified in Sector Count / LBA registers.
If the RANGE bit is not set, or the implementation does not support the
RANGE bit, then the FLUSH CACHE operation shall flush the entire cache.

Sector Count -
Maximum number of sectors to be flushed from the cache. A value of 00h
specified that 256 sectors are to be flushed.

LBA Low / Mid / High -
An LBA starting address for the flush. Register contents as specified
in READ DMA command, and other commands.

Normal outputs:
---------------
Unchanged.

Error outputs:
--------------
Error register -

RANGE (bit 0) shall be set to one, if RANGE bit was specified in
Features register when the command was submitted, indicating this was a
range-based flush cache.

Description
-----------
If RANGE bit is set to one, the flush cache operation at a minimum shall
flush the specified range of sectors specified by LBA / Sector Count.
An implementation may choose to flush more than the specified range, up
to an entire cache flush in a compatible or "no op" implementation.

If no data within the specified LBA range exists in cache to be flushed,
that shall not be considered an error.

4) Modify FLUSH CACHE EXT (EAh) as follows:

Inputs:
-------

Features:
curr bit 0 (RANGE)
prev na
Sector Count:
curr sector count(7:0)
prev sector count(15:8)
LBA Low:
curr LBA(7:0)
prev LBA(31:24)
LBA Mid:
curr LBA(15:8)
prev LBA(39:32)
LBA High:
curr LBA(23:16)
prev LBA(47:40)

Features -
If the RANGE bit is set, the cache flush operation shall be considered
to be limited to the region specified in Sector Count / LBA registers.
If the RANGE bit is not set, or the implementation does not support the
RANGE bit, then the FLUSH CACHE operation shall flush the entire cache.

Sector Count -
Maximum number of sectors to be flushed from the cache. A value of
0000h specified that 65,536 sectors are to be flushed.

LBA Low / Mid / High -
An LBA starting address for the flush. Register contents as specified
in READ DMA command, and other commands.

Normal outputs:
---------------
Unchanged.

Error outputs:
--------------
Error register -

RANGE (bit 0) shall be set to one, if RANGE bit was specified in
Features register when the command was submitted, indicating this was a
range-based flush cache.

Description
-----------
If RANGE bit is set to one, the flush cache operation at a minimum shall
flush the specified range of sectors specified by LBA / Sector Count.
An implementation may choose to flush more than the specified range, up
to an entire cache flush in a compatible or "no op" implementation.

If no data within the specified LBA range exists in cache to be flushed,
that shall not be considered an error.

</proposal>

Comments requested.

We need to KISS, if this proposal has any hope getting accepted.

People interested in filesystem journalling, barriers and such please
review.

Once people on lkml are happy, I'll write this up in a PDF in T13 form,
and propose it on the T13 list (making sure everyone involved is
properly credited, of course).

Jeff