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

From: "Ulrich Windl" <Ulrich.Windl@rz.uni-regensburg.de>
To: <zzam@gentoo.org>, <hdegoede@redhat.com>, <stern@rowland.harvard.edu>
Cc: "systemd-devel@lists.freedesktop.org" 
	<systemd-devel@lists.freedesktop.org>,
	<usb-storage@lists.one-eyed-alien.net>,
	<hirofumi@mail.parknet.co.jp>, <linux-usb@vger.kernel.org>
Subject: Antw: [EXT] Re: [systemd-devel] [usb-storage] Re: Amazon Kindle disconnect after Synchronize Cache
Date: Thu, 18 Mar 2021 08:04:43 +0100	[thread overview]
Message-ID: <6052FB8B020000A10003FE28@gwsmtp.uni-regensburg.de> (raw)
In-Reply-To: <474C42CD02000091AE14D9EC@gwsmtp.uni-regensburg.de>

>>> Matthias Schwarzott <zzam@gentoo.org> schrieb am 17.03.2021 um 18:56 in
Nachricht <5f8c0755-0884-f505-c4e8-3a5e89001d58@gentoo.org>:
> 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.

...once you have the right kernel

> 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
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