From: Robin Murphy <robin.murphy@arm.com>
To: Kim Phillips <kim.phillips@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, mathieu.poirier@linaro.org,
mike.leach@linaro.org, robert.walker@arm.com,
mark.rutland@arm.com, will.deacon@arm.com, sudeep.holla@arm.com,
frowand.list@gmail.com, robh@kernel.org, john.horley@arm.com
Subject: Re: [PATCH v2 21/27] coresight: Convert driver messages to dev_dbg
Date: Wed, 2 May 2018 14:52:43 +0100 [thread overview]
Message-ID: <adf2465b-dd2c-dc0f-51ca-da7f1a8836ba@arm.com> (raw)
In-Reply-To: <20180501225503.a55fb963795afb40163f3763@arm.com>
On 02/05/18 04:55, Kim Phillips wrote:
> On Tue, 1 May 2018 10:10:51 +0100
> Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>
>> Convert component enable/disable messages from dev_info to dev_dbg.
>> This is required to prevent LOCKDEP splats when operating in perf
>> mode where we could be called with locks held to enable a coresight
>
> Can we see the splats? Doesn't lockdep turn itself off if it starts
> triggering too many splats?
Without some very careful and robust reasoning for why the condition
being reported by lockdep could not actually occur in practice,
"avoiding the splats" is far, far less important than "avoiding the
potential deadlock that they are reporting".
>> path. If someone wants to really see the messages, they can always
>> enable it at runtime via dynamic_debug.
>
> Won't the splats still occur when the messages are enabled with
> dynamic_debug?
>
> So in effect this patch only tries to mitigate the splats, all the
> while making things harder for regular users that now have to recompile
> their kernels, in exchange for a very small convenience for kernel
> developers that happen to see a splat or two with DEBUG_LOCKDEP set?
FWIW, if "regular users" means people running distro kernels, then
chances are that they probably have DYNAMIC_DEBUG set already (100% of
my local sample of 2 - Ubuntu x86_64 and Arch aarch64 - certainly do).
Either way, though, this particular log spam really does only look
vaguely useful to people debugging the coresight stack itself, so anyone
going out of their way to turn it on has surely already gone beyond
regular use (even if they're just reproducing an issue with additional
logging at the request of kernel developers, rather than debugging it
themselves).
Reducing the scope for possible deadlock from the general case to just
debugging scenarios is certainly not a bad thing, but as you say I think
we need a closer look at the underlying issue to know whether even
dev_dbg() is wise.
Robin.
WARNING: multiple messages have this Message-ID (diff)
From: robin.murphy@arm.com (Robin Murphy)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 21/27] coresight: Convert driver messages to dev_dbg
Date: Wed, 2 May 2018 14:52:43 +0100 [thread overview]
Message-ID: <adf2465b-dd2c-dc0f-51ca-da7f1a8836ba@arm.com> (raw)
In-Reply-To: <20180501225503.a55fb963795afb40163f3763@arm.com>
On 02/05/18 04:55, Kim Phillips wrote:
> On Tue, 1 May 2018 10:10:51 +0100
> Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>
>> Convert component enable/disable messages from dev_info to dev_dbg.
>> This is required to prevent LOCKDEP splats when operating in perf
>> mode where we could be called with locks held to enable a coresight
>
> Can we see the splats? Doesn't lockdep turn itself off if it starts
> triggering too many splats?
Without some very careful and robust reasoning for why the condition
being reported by lockdep could not actually occur in practice,
"avoiding the splats" is far, far less important than "avoiding the
potential deadlock that they are reporting".
>> path. If someone wants to really see the messages, they can always
>> enable it at runtime via dynamic_debug.
>
> Won't the splats still occur when the messages are enabled with
> dynamic_debug?
>
> So in effect this patch only tries to mitigate the splats, all the
> while making things harder for regular users that now have to recompile
> their kernels, in exchange for a very small convenience for kernel
> developers that happen to see a splat or two with DEBUG_LOCKDEP set?
FWIW, if "regular users" means people running distro kernels, then
chances are that they probably have DYNAMIC_DEBUG set already (100% of
my local sample of 2 - Ubuntu x86_64 and Arch aarch64 - certainly do).
Either way, though, this particular log spam really does only look
vaguely useful to people debugging the coresight stack itself, so anyone
going out of their way to turn it on has surely already gone beyond
regular use (even if they're just reproducing an issue with additional
logging at the request of kernel developers, rather than debugging it
themselves).
Reducing the scope for possible deadlock from the general case to just
debugging scenarios is certainly not a bad thing, but as you say I think
we need a closer look at the underlying issue to know whether even
dev_dbg() is wise.
Robin.
next prev parent reply other threads:[~2018-05-02 13:52 UTC|newest]
Thread overview: 134+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-01 9:10 [PATCH v2 00/27] coresight: TMC ETR backend support for perf Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 01/27] coresight: ETM: Add support for ARM Cortex-A73 Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 02/27] coresight: Cleanup device subtype struct Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 03/27] coresight: Add helper device type Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-03 17:00 ` Mathieu Poirier
2018-05-03 17:00 ` Mathieu Poirier
2018-05-05 9:56 ` Suzuki K Poulose
2018-05-05 9:56 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 04/27] coresight: Introduce support for Coresight Addrss Translation Unit Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-03 17:31 ` Mathieu Poirier
2018-05-03 17:31 ` Mathieu Poirier
2018-05-03 20:25 ` Mathieu Poirier
2018-05-03 20:25 ` Mathieu Poirier
2018-05-05 10:03 ` Suzuki K Poulose
2018-05-05 10:03 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 05/27] dts: bindings: Document device tree binding for CATU Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 13:10 ` Rob Herring
2018-05-01 13:10 ` Rob Herring
2018-05-03 17:42 ` Mathieu Poirier
2018-05-03 17:42 ` Mathieu Poirier
2018-05-08 15:40 ` Suzuki K Poulose
2018-05-08 15:40 ` Suzuki K Poulose
2018-05-11 16:05 ` Rob Herring
2018-05-11 16:05 ` Rob Herring
2018-05-14 14:42 ` Mathieu Poirier
2018-05-14 14:42 ` Mathieu Poirier
2018-05-01 9:10 ` [PATCH v2 06/27] coresight: tmc etr: Disallow perf mode temporarily Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 07/27] coresight: tmc: Hide trace buffer handling for file read Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-03 19:50 ` Mathieu Poirier
2018-05-03 19:50 ` Mathieu Poirier
2018-05-01 9:10 ` [PATCH v2 08/27] coresight: tmc-etr: Do not clean trace buffer Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 09/27] coresight: Add helper for inserting synchronization packets Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 10/27] dts: bindings: Restrict coresight tmc-etr scatter-gather mode Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 13:13 ` Rob Herring
2018-05-01 13:13 ` Rob Herring
2018-05-03 20:32 ` Mathieu Poirier
2018-05-03 20:32 ` Mathieu Poirier
2018-05-04 22:56 ` Rob Herring
2018-05-04 22:56 ` Rob Herring
2018-05-08 15:48 ` Suzuki K Poulose
2018-05-08 15:48 ` Suzuki K Poulose
2018-05-08 17:34 ` Rob Herring
2018-05-08 17:34 ` Rob Herring
2018-05-01 9:10 ` [PATCH v2 11/27] dts: juno: Add scatter-gather support for all revisions Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 12/27] coresight: tmc-etr: Allow commandline option to override SG use Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-03 20:40 ` Mathieu Poirier
2018-05-03 20:40 ` Mathieu Poirier
2018-05-08 15:49 ` Suzuki K Poulose
2018-05-08 15:49 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 13/27] coresight: Add generic TMC sg table framework Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-04 17:35 ` Mathieu Poirier
2018-05-04 17:35 ` Mathieu Poirier
2018-05-01 9:10 ` [PATCH v2 14/27] coresight: Add support for TMC ETR SG unit Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 15/27] coresight: tmc-etr: Make SG table circular Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 16/27] coresight: tmc-etr: Add transparent buffer management Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-07 17:20 ` Mathieu Poirier
2018-05-07 17:20 ` Mathieu Poirier
2018-05-01 9:10 ` [PATCH v2 17/27] coresight: etr: Add support for save restore buffers Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-07 17:48 ` Mathieu Poirier
2018-05-07 17:48 ` Mathieu Poirier
2018-05-01 9:10 ` [PATCH v2 18/27] coresight: catu: Add support for scatter gather tables Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-07 20:25 ` Mathieu Poirier
2018-05-07 20:25 ` Mathieu Poirier
2018-05-08 15:56 ` Suzuki K Poulose
2018-05-08 15:56 ` Suzuki K Poulose
2018-05-08 16:13 ` Mathieu Poirier
2018-05-08 16:13 ` Mathieu Poirier
2018-05-01 9:10 ` [PATCH v2 19/27] coresight: catu: Plug in CATU as a backend for ETR buffer Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-07 22:02 ` Mathieu Poirier
2018-05-07 22:02 ` Mathieu Poirier
2018-05-08 16:21 ` Suzuki K Poulose
2018-05-08 16:21 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 20/27] coresight: tmc: Add configuration support for trace buffer size Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 21/27] coresight: Convert driver messages to dev_dbg Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-02 3:55 ` Kim Phillips
2018-05-02 3:55 ` Kim Phillips
2018-05-02 8:25 ` Robert Walker
2018-05-02 8:25 ` Robert Walker
2018-05-02 13:52 ` Robin Murphy [this message]
2018-05-02 13:52 ` Robin Murphy
2018-05-10 13:36 ` Suzuki K Poulose
2018-05-10 13:36 ` Suzuki K Poulose
2018-05-07 22:28 ` Mathieu Poirier
2018-05-07 22:28 ` Mathieu Poirier
2018-05-01 9:10 ` [PATCH v2 22/27] coresight: tmc-etr: Track if the device is coherent Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 23/27] coresight: tmc-etr: Handle driver mode specific ETR buffers Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-08 17:18 ` Mathieu Poirier
2018-05-08 17:18 ` Mathieu Poirier
2018-05-08 21:51 ` Suzuki K Poulose
2018-05-08 21:51 ` Suzuki K Poulose
2018-05-09 17:12 ` Mathieu Poirier
2018-05-09 17:12 ` Mathieu Poirier
2018-05-01 9:10 ` [PATCH v2 24/27] coresight: tmc-etr: Relax collection of trace from sysfs mode Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-07 22:54 ` Mathieu Poirier
2018-05-07 22:54 ` Mathieu Poirier
2018-05-01 9:10 ` [PATCH v2 25/27] coresight: etr_buf: Add helper for padding an area of trace data Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-08 17:34 ` Mathieu Poirier
2018-05-08 17:34 ` Mathieu Poirier
2018-05-01 9:10 ` [PATCH v2 26/27] coresight: perf: Remove reset_buffer call back for sinks Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-08 19:42 ` Mathieu Poirier
2018-05-08 19:42 ` Mathieu Poirier
2018-05-11 16:35 ` Suzuki K Poulose
2018-05-11 16:35 ` Suzuki K Poulose
2018-05-01 9:10 ` [PATCH v2 27/27] coresight: etm-perf: Add support for ETR backend Suzuki K Poulose
2018-05-01 9:10 ` Suzuki K Poulose
2018-05-08 22:04 ` Mathieu Poirier
2018-05-08 22:04 ` Mathieu Poirier
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