[systemd-devel] [usb-storage] Re: Amazon Kindle disconnect after Synchronize Cache

[Hans de Goede]

Hi,

On 3/17/21 6:56 PM, Matthias Schwarzott wrote:
> Am 17.03.21 um 16:17 schrieb Alan Stern:
>> On Wed, Mar 17, 2021 at 01:21:50PM +0100, Hans de Goede wrote:
>>> Hi,
>>>
>>> On 3/16/21 6:04 PM, Alan Stern wrote:
>>>> I think it would be mildly better, but not a whole lot.  Since the
>>>> Kindle describes itself as having removable media, the kernel normally
>>>> probes it periodically to make sure the media remains present.  The
>>>> default probing interval is 2 seconds.  Reducing it to 0.9 seconds
>>>> doesn't represent an exorbitant additional load IMO -- especially since
>>>> Kindles don't tend to spend huge amounts of time connected to computers.
>>>
>>> Ah, I did not know that the default polling interval was that low(ish),
>>> given that the default indeed is already that low, then changing it to
>>> 0.8 seconds would not be a big change.  And we probably have a lot of
>>> lower hanging fruit for unnecessary wakeups then that.
>>
>> So we need to make a decision: Should the patch be merged, or should we
>> punt the issue to userspace tools?
>>
>> On the plus side, the patch is rather small and non-invasive (although
>> it does allocate the last remaining bit in the 32-bit fflags field).
>> There's also the advantage of sending the extra command only when it is
>> needed, as opposed to increasing the overall frequency of TUR polling.
>>
>> Any opinions?
> 
> I would vote to do in kernel as that is a cleaner solution:
> 
> 1. It will work out of the box.
> 2. It only sends one extra command when needed.
> 3. It makes the block-device not break if user-space adjusts the poll interval to higher values.

FWIW my vote goes to the in kernel fix too.

Regards,

Hans