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

[Matthias Schwarzott]

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.

Matthias