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From: Dan Williams <dan.j.williams@intel.com>
To: "Kani, Toshimitsu" <toshi.kani@hpe.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>
Subject: Re: [PATCH] libnvdimm: rework region badblocks clearing
Date: Mon, 1 May 2017 08:52:22 -0700	[thread overview]
Message-ID: <CAPcyv4gxuez8BvtWwwcTXCKpzKp+oGQrRQG8+2iQ6XqRAfT_3g@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4g4G_fJf6OOGpWbpyMdNioPWEFoJ2eO7+dSTcep+OerFw@mail.gmail.com>

On Mon, May 1, 2017 at 8:43 AM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Mon, May 1, 2017 at 8:34 AM, Kani, Toshimitsu <toshi.kani@hpe.com> wrote:
>> On Sun, 2017-04-30 at 05:39 -0700, Dan Williams wrote:
>>> Toshi noticed that the new support for a region-level badblocks
>>> missed the case where errors are cleared due to BTT I/O.
>>>
>>> An initial attempt to fix this ran into a "sleeping while atomic"
>>> warning due to taking the nvdimm_bus_lock() in the BTT I/O path to
>>> satisfy the locking requirements of __nvdimm_bus_badblocks_clear().
>>> However, that lock is not needed since we are not acting any data
>>> that is subject to change due to a change of state of the bus /
>>> region. The badblocks instance has its own internal lock to handle
>>> mutations of the error list.
>>>
>>> So, to make it clear that we are just acting on region devices and
>>> don't need the lock rename __nvdimm_bus_badblocks_clear() to
>>> nvdimm_clear_badblocks_regions(). Eliminate the lock and consolidate
>>> all routines in drivers/nvdimm/bus.c. Also, make some cleanups to
>>> remove unnecessary casts, make the calling convention of
>>> nvdimm_clear_badblocks_regions() clearer by replacing struct resource
>>> with the minimal struct clear_badblocks_context, and use the
>>> DEVICE_ATTR macro.
>>
>> Hi Dan,
>>
>> I was testing the change with CONFIG_DEBUG_ATOMIC_SLEEP set this time,
>> and hit the following BUG with BTT.  This is a separate issue (not
>> introduced by this patch), but it shows that we have an issue with the
>> DSM call path as well.
>
> Ah, great find, thanks! We don't see this in the unit tests because
> the nfit_test infrastructure takes no sleeping actions in its
> simulated DSM path. Outside of converting btt to use sleeping locks
> I'm not sure I see a path forward. I wonder how bad the performance
> impact of that would be? Perhaps with opportunistic spinning it won't
> be so bad, but I don't see another choice.

It's worse than that. Part of the performance optimization of BTT I/O
was to avoid locking altogether when we could rely on a BTT lane
percpu, so that would also need to be removed.
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm

WARNING: multiple messages have this Message-ID (diff)
From: Dan Williams <dan.j.williams@intel.com>
To: "Kani, Toshimitsu" <toshi.kani@hpe.com>
Cc: "linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	"Verma, Vishal L" <vishal.l.verma@intel.com>
Subject: Re: [PATCH] libnvdimm: rework region badblocks clearing
Date: Mon, 1 May 2017 08:52:22 -0700	[thread overview]
Message-ID: <CAPcyv4gxuez8BvtWwwcTXCKpzKp+oGQrRQG8+2iQ6XqRAfT_3g@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4g4G_fJf6OOGpWbpyMdNioPWEFoJ2eO7+dSTcep+OerFw@mail.gmail.com>

On Mon, May 1, 2017 at 8:43 AM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Mon, May 1, 2017 at 8:34 AM, Kani, Toshimitsu <toshi.kani@hpe.com> wrote:
>> On Sun, 2017-04-30 at 05:39 -0700, Dan Williams wrote:
>>> Toshi noticed that the new support for a region-level badblocks
>>> missed the case where errors are cleared due to BTT I/O.
>>>
>>> An initial attempt to fix this ran into a "sleeping while atomic"
>>> warning due to taking the nvdimm_bus_lock() in the BTT I/O path to
>>> satisfy the locking requirements of __nvdimm_bus_badblocks_clear().
>>> However, that lock is not needed since we are not acting any data
>>> that is subject to change due to a change of state of the bus /
>>> region. The badblocks instance has its own internal lock to handle
>>> mutations of the error list.
>>>
>>> So, to make it clear that we are just acting on region devices and
>>> don't need the lock rename __nvdimm_bus_badblocks_clear() to
>>> nvdimm_clear_badblocks_regions(). Eliminate the lock and consolidate
>>> all routines in drivers/nvdimm/bus.c. Also, make some cleanups to
>>> remove unnecessary casts, make the calling convention of
>>> nvdimm_clear_badblocks_regions() clearer by replacing struct resource
>>> with the minimal struct clear_badblocks_context, and use the
>>> DEVICE_ATTR macro.
>>
>> Hi Dan,
>>
>> I was testing the change with CONFIG_DEBUG_ATOMIC_SLEEP set this time,
>> and hit the following BUG with BTT.  This is a separate issue (not
>> introduced by this patch), but it shows that we have an issue with the
>> DSM call path as well.
>
> Ah, great find, thanks! We don't see this in the unit tests because
> the nfit_test infrastructure takes no sleeping actions in its
> simulated DSM path. Outside of converting btt to use sleeping locks
> I'm not sure I see a path forward. I wonder how bad the performance
> impact of that would be? Perhaps with opportunistic spinning it won't
> be so bad, but I don't see another choice.

It's worse than that. Part of the performance optimization of BTT I/O
was to avoid locking altogether when we could rely on a BTT lane
percpu, so that would also need to be removed.

  reply	other threads:[~2017-05-01 15:52 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-30 12:39 [PATCH] libnvdimm: rework region badblocks clearing Dan Williams
2017-04-30 12:39 ` Dan Williams
2017-05-01 15:34 ` Kani, Toshimitsu
2017-05-01 15:34   ` Kani, Toshimitsu
2017-05-01 15:43   ` Dan Williams
2017-05-01 15:43     ` Dan Williams
2017-05-01 15:52     ` Dan Williams [this message]
2017-05-01 15:52       ` Dan Williams
2017-05-01 16:12       ` Kani, Toshimitsu
2017-05-01 16:12         ` Kani, Toshimitsu
2017-05-01 16:16         ` Dan Williams
2017-05-01 16:16           ` Dan Williams
2017-05-01 16:20           ` Kani, Toshimitsu
2017-05-01 16:20             ` Kani, Toshimitsu
2017-05-01 16:38             ` Dan Williams
2017-05-01 16:38               ` Dan Williams
2017-05-01 16:42               ` Verma, Vishal L
2017-05-01 16:42                 ` Verma, Vishal L
2017-05-01 16:45                 ` Kani, Toshimitsu
2017-05-01 16:45                   ` Kani, Toshimitsu
2017-05-01 21:26 ` Kani, Toshimitsu
2017-05-01 21:26   ` Kani, Toshimitsu
2017-05-01 23:09   ` Dan Williams
2017-05-01 23:09     ` Dan Williams

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