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Message-ID: <CAKF3qh3nBS=bbusT_na54qo-yBdM1vc38Lx7JGm0Ck2sZ6qoCA@mail.gmail.com>
Date: Tue, 29 Sep 2020 10:28:08 +0800
From: Ethan Zhao <xerces.zhao@...il.com>
To: "Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@...el.com>
Cc: Sinan Kaya <okaya@...nel.org>,
"Zhao, Haifeng" <haifeng.zhao@...el.com>,
"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
"oohall@...il.com" <oohall@...il.com>,
"ruscur@...sell.cc" <ruscur@...sell.cc>,
"lukas@...ner.de" <lukas@...ner.de>,
"andriy.shevchenko@...ux.intel.com"
<andriy.shevchenko@...ux.intel.com>,
"stuart.w.hayes@...il.com" <stuart.w.hayes@...il.com>,
"mr.nuke.me@...il.com" <mr.nuke.me@...il.com>,
"mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
Keith Busch <keith.busch@...el.com>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Jia, Pei P" <pei.p.jia@...el.com>,
"ashok.raj@...ux.intel.com" <ashok.raj@...ux.intel.com>
Subject: Re: [PATCH 2/5 V2] PCI: pciehp: check and wait port status out of DPC
before handling DLLSC and PDC
On Tue, Sep 29, 2020 at 12:45 AM Kuppuswamy, Sathyanarayanan
<sathyanarayanan.kuppuswamy@...el.com> wrote:
>
>
> On 9/28/20 9:43 AM, Sinan Kaya wrote:
> > On 9/28/2020 7:10 AM, Sinan Kaya wrote:
> >> On 9/27/2020 10:01 PM, Zhao, Haifeng wrote:
> >>> Sinan,
> >>> I explained the reason why locks don't protect this case in the patch description part.
> >>> Write side and read side hold different semaphore and mutex.
> >>>
> >> I have been thinking about it some time but is there any reason why we
> >> have to handle all port AER/DPC/HP events in different threads?
> >>
> >> Can we go to single threaded event loop for all port drivers events?
> >>
> >> This will require some refactoring but it wlll eliminate the lock
> >> nightmares we are having.
> >>
> >> This means no sleeping. All sleeps need to happen outside of the loop.
> >>
> >> I wanted to see what you all are thinking about this.
> >>
> >> It might become a performance problem if the system is
> >> continuously observing a hotplug/aer/dpc events.
> >>
> >> I always think that these should be rare events.
> > If restructuring would be too costly, the preferred solution should be
> > to fix the locks in hotplug driver rather than throwing there a random
> > wait call.
> Since the current race condition is detected between DPC and
> hotplug, I recommend synchronizing them.
The locks are the first place to root cause and try to fix. but not so easy to
refactor the remove-scan-semaphore and the bus-walk-mutex. too expensive
work. --- rework every piece of code that uses them.
Thanks,
Ethan
>
> --
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer
>
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