Re: [PATCH] mmc: core: add auto bkops support
From: Shawn Lin
Date: Wed Jun 22 2016 - 22:08:32 EST
å 2016/6/22 18:21, Ulf Hansson åé:
On 13 June 2016 at 14:25, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
On 13/06/16 11:58, Shawn Lin wrote:
å 2016/6/13 16:17, Adrian Hunter åé:
On 13/06/16 10:48, Shawn Lin wrote:
On 2016/6/13 14:29, Adrian Hunter wrote:
On 06/06/16 06:07, Shawn Lin wrote:
JEDEC eMMC v5.1 introduce an autonomously initiated method
for background operations.
Host that wants to enable the device to perform background
operations during device idle time, should signal the device
by setting AUTO_EN in BKOPS_EN field EXT_CSD[163] to 1b. When
this bit is set, the device may start or stop background operations
whenever it sees fit, without any notification to the host.
When AUTO_EN bit is set, the host should keep the device power
active. The host may set or clear this bit at any time based on
its power constraints or other considerations.
Currently the manual bkops is only be used under the async req
circumstances and it's a bit complicated to be controlled as the
perfect method is that we should do some idle monitor just as rpm
and send HPI each time if receiving rd/wr req. But it will impact
performance significantly, especially for random iops since the
weight of executing HPI against r/w small piece of LBAs is
nonnegligible.
So we now prefer to select the auto one unconditionally if supported
which makes it as simple as possible. It should really good enough
for devices to manage its internal policy for bkops rather than the
host, which makes us believe that we could achieve the best
performance for all the devices implementing auto bkops and the only
thing we should do is to disable it when cutting off the power.
Do you know if there is really a requirement to do that?
Even without bkops enable, no matter for manual or auto one, FTL should
always do bkops like GC internally when needed to guarantee the
performance and balance the wear leveling. What I thought to do is to
make it more explicitly.
Because then, what
is the point of power off notification?
When power off notification is sent, bkops will be stopped
in _mmc_suspend. So I don't undertand your point here?
I am trying to understand why we need to do anything for auto bkops.
Since AUTO_EN is persistent, we can leave the decision whether to turn it on
to whomever provisions the device. Then we just leave it alone.
Hrm..
one possible way is to control it by mmc-utils on
user space? So we should add a cmd for mmc-utils
there?
That would be consistent with manual bkops.
From my first impression I agree, as that is the policy we have been
sticking to when writing to persistent EXT_CSD persistent .
Although, in this case, I am actually wondering on what is the best approach.
I don't know what is the real meaning of "persistent". :)
I don't know should we count auto bkops as the persistent
registers....HS_TIMING and BUS_WIDTH should also be persistent
registers as them are always used after initialization if not changing
them?
IHMO the more reasonable way is that:
IIRC many settings for EXT_CSD should be OTP, like hw-reset(162),
reliable write(167) fw-configure(169)..etc, which are marked as R/W.
These should be controlled by userpace or even by firmware when
flashing emmc, like reliable write...
I'm not sure whether should I updete this $SUBJUCT or migirating it to
userspace... We need to come to an agreement :)
Is there really ever a case when we don't want auto BKOPS to be default enabled?
I think BKOPS is a fundamental feature of an FTL and I can't see a
reason to why we need to involve mmc-utils/userspace to enable it. Am
I wrong?
Kind regards
Uffe
--
Best Regards
Shawn Lin