Re: [PATCH] hw/scsi/lsi53c895a: add hack to prevent scsi timeouts in HP-UX 10.20

From: Sven Schnelle <svens@stackframe.org>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,  Fam Zheng <fam@euphon.net>,
	qemu-devel@nongnu.org,  deller@gmx.de
Subject: Re: [PATCH] hw/scsi/lsi53c895a: add hack to prevent scsi timeouts in HP-UX 10.20
Date: Thu, 29 Feb 2024 19:01:53 +0100	[thread overview]
Message-ID: <87msrjxi7i.fsf@t14.stackframe.org> (raw)
In-Reply-To: <CAFEAcA8tbtrtoZSO2MmLHr+7+mcys63z15qFEVYm=nAO4cUMmQ@mail.gmail.com> (Peter Maydell's message of "Thu, 29 Feb 2024 17:26:53 +0000")

Peter Maydell <peter.maydell@linaro.org> writes:

> On Thu, 29 Feb 2024 at 16:54, Sven Schnelle <svens@stackframe.org> wrote:
>>
>> Peter Maydell <peter.maydell@linaro.org> writes:
>>
>> > On Wed, 28 Feb 2024 at 21:12, Sven Schnelle <svens@stackframe.org> wrote:
>> >>
>> >> HP-UX 10.20 seems to make the lsi53c895a spinning on a memory location
>> >> under certain circumstances. As the SCSI controller and CPU are not
>> >> running at the same time this loop will never finish. After some
>> >> time, the check loop interrupts with a unexpected device disconnect.
>> >> This works, but is slow because the kernel resets the scsi controller.
>> >> Instead of signaling UDC, add an option 'hpux-spin-workaround' which
>> >> emulates a INTERRUPT 2 script instruction. This instruction tells the
>> >> kernel that the request was fulfilled. With this change, SCSI speeds
>> >> improves significantly.
>> >> [..]
>> > I see we already have a hacky workaround for other OSes
>> > that do something similar. The ideal fix for both of these
>> > I think would be for lsi_execute_script() to, instead of stopping,
>> > arrange to defer executing more script instructions until
>> > after the guest has had a chance to run a bit more.
>> > I think setting a timer that calls lsi_resume_script() after
>> > a while would have that effect.
>>
>> Thanks, good idea. So something like this?
>
> Yeah, something like that I think. (You probably want to delete
> the timer on reset, and you need to handle migration -- you can
> either put the timer state in a new vmstate section, or else
> in post-load if the state is 'LSI_WAIT_SCRIPTS' arm the timer.)

> Does it work? :-)

Yes it does. I only did a quick hack without caring about things like
reset, freeing the timer and migration. I successfully booted HP-UX 10.20
without any scsi errors in the dmesg. So i think this is much better
than the commandline option. I'll prepare a proper patch in the next
days and submit it.

Thanks!
Sven