From: Robin Murphy <robin.murphy@arm.com>
To: Huang Shijie <shijie.huang@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>,
iommu@lists.linux-foundation.org, will.deacon@arm.com,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL
Date: Wed, 20 Jan 2016 14:46:34 +0000 [thread overview]
Message-ID: <569F9DCA.3030808@arm.com> (raw)
In-Reply-To: <20160120133401.GA3487@localhost.localdomain>
On 20/01/16 13:34, Huang Shijie wrote:
> On Wed, Jan 20, 2016 at 01:02:25PM +0100, Joerg Roedel wrote:
>> On Tue, Jan 12, 2016 at 10:15:05AM +0800, Huang Shijie wrote:
>>> This patch adds a shortcut for the code when the @device_node is NULL.
>>> In my juno-r1 board, the boot time can be faster by 0.004014s.
>>
>> How have you made sure this number is reliable and not just noise in the
>> boot process?
> In the boot process, there are 5 or more modules whose @dev_node are
> NULL. Without the patch, the kernel will waste some cycles to do the
> meaningless calculations for all these modules.
With a quick counting hack, booting 4.4 on my r1 indeed shows 5 calls
where dev_node is null. Plus 68 calls in which we waste cycles doing
meaningless calculations when dev_node is non-null. The fundamental
issue at hand is that the "platform bus" is a rubbish abstraction.
> In theory, it is not noise.
> If you have interest, I can send you the kernel boot logs. :)
>
> Of course, the 0.004014s maybe not accurate enough, it is just an
> approximate number.
A mean and standard deviation of at least, say, 5 runs each with and
without the patch would be considerably more meaningful (even if still
far from statistically significant).
Robin.
>
> Thanks
> Huang Shijie
>
> _______________________________________________
> iommu mailing list
> iommu@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>
WARNING: multiple messages have this Message-ID (diff)
From: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>
To: Huang Shijie <shijie.huang-5wv7dgnIgG8@public.gmane.org>
Cc: will.deacon-5wv7dgnIgG8@public.gmane.org,
iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org,
linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL
Date: Wed, 20 Jan 2016 14:46:34 +0000 [thread overview]
Message-ID: <569F9DCA.3030808@arm.com> (raw)
In-Reply-To: <20160120133401.GA3487-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
On 20/01/16 13:34, Huang Shijie wrote:
> On Wed, Jan 20, 2016 at 01:02:25PM +0100, Joerg Roedel wrote:
>> On Tue, Jan 12, 2016 at 10:15:05AM +0800, Huang Shijie wrote:
>>> This patch adds a shortcut for the code when the @device_node is NULL.
>>> In my juno-r1 board, the boot time can be faster by 0.004014s.
>>
>> How have you made sure this number is reliable and not just noise in the
>> boot process?
> In the boot process, there are 5 or more modules whose @dev_node are
> NULL. Without the patch, the kernel will waste some cycles to do the
> meaningless calculations for all these modules.
With a quick counting hack, booting 4.4 on my r1 indeed shows 5 calls
where dev_node is null. Plus 68 calls in which we waste cycles doing
meaningless calculations when dev_node is non-null. The fundamental
issue at hand is that the "platform bus" is a rubbish abstraction.
> In theory, it is not noise.
> If you have interest, I can send you the kernel boot logs. :)
>
> Of course, the 0.004014s maybe not accurate enough, it is just an
> approximate number.
A mean and standard deviation of at least, say, 5 runs each with and
without the patch would be considerably more meaningful (even if still
far from statistically significant).
Robin.
>
> Thanks
> Huang Shijie
>
> _______________________________________________
> iommu mailing list
> iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>
WARNING: multiple messages have this Message-ID (diff)
From: robin.murphy@arm.com (Robin Murphy)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL
Date: Wed, 20 Jan 2016 14:46:34 +0000 [thread overview]
Message-ID: <569F9DCA.3030808@arm.com> (raw)
In-Reply-To: <20160120133401.GA3487@localhost.localdomain>
On 20/01/16 13:34, Huang Shijie wrote:
> On Wed, Jan 20, 2016 at 01:02:25PM +0100, Joerg Roedel wrote:
>> On Tue, Jan 12, 2016 at 10:15:05AM +0800, Huang Shijie wrote:
>>> This patch adds a shortcut for the code when the @device_node is NULL.
>>> In my juno-r1 board, the boot time can be faster by 0.004014s.
>>
>> How have you made sure this number is reliable and not just noise in the
>> boot process?
> In the boot process, there are 5 or more modules whose @dev_node are
> NULL. Without the patch, the kernel will waste some cycles to do the
> meaningless calculations for all these modules.
With a quick counting hack, booting 4.4 on my r1 indeed shows 5 calls
where dev_node is null. Plus 68 calls in which we waste cycles doing
meaningless calculations when dev_node is non-null. The fundamental
issue at hand is that the "platform bus" is a rubbish abstraction.
> In theory, it is not noise.
> If you have interest, I can send you the kernel boot logs. :)
>
> Of course, the 0.004014s maybe not accurate enough, it is just an
> approximate number.
A mean and standard deviation of at least, say, 5 runs each with and
without the patch would be considerably more meaningful (even if still
far from statistically significant).
Robin.
>
> Thanks
> Huang Shijie
>
> _______________________________________________
> iommu mailing list
> iommu at lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>
next prev parent reply other threads:[~2016-01-20 14:46 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-12 2:15 [PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL Huang Shijie
2016-01-12 2:15 ` Huang Shijie
2016-01-12 2:15 ` Huang Shijie
2016-01-20 12:02 ` Joerg Roedel
2016-01-20 12:02 ` Joerg Roedel
2016-01-20 12:02 ` Joerg Roedel
2016-01-20 13:34 ` Huang Shijie
2016-01-20 13:34 ` Huang Shijie
2016-01-20 13:34 ` Huang Shijie
2016-01-20 14:46 ` Robin Murphy [this message]
2016-01-20 14:46 ` Robin Murphy
2016-01-20 14:46 ` Robin Murphy
2016-01-20 16:00 ` Jon Medhurst (Tixy)
2016-01-20 16:00 ` Jon Medhurst (Tixy)
2016-01-21 2:04 ` Huang Shijie
2016-01-21 2:04 ` Huang Shijie
2016-01-21 2:04 ` Huang Shijie
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