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Groups > linux.kernel > #1313264
| From | Robin Murphy <robin.murphy@arm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL |
| Date | 2016-01-20 15:50 +0100 |
| Message-ID | <qT2f7-7Ty-9@gated-at.bofh.it> (permalink) |
| References | <qSZKi-68m-7@gated-at.bofh.it> <qSZKi-68m-5@gated-at.bofh.it> <qT19p-78z-13@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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 >
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Re: [PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL Joerg Roedel <joro@8bytes.org> - 2016-01-20 13:10 +0100
Re: [PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL Huang Shijie <shijie.huang@arm.com> - 2016-01-20 14:40 +0100
Re: [PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL Robin Murphy <robin.murphy@arm.com> - 2016-01-20 15:50 +0100
Re: [PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL "Jon Medhurst (Tixy)" <tixy@linaro.org> - 2016-01-20 17:10 +0100
Re: [PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL Huang Shijie <shijie.huang@arm.com> - 2016-01-21 03:10 +0100
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