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Wysocki" Date: Thu, 13 Feb 2020 11:17:11 +0100 Message-ID: Subject: Re: [PATCH 00/28] PM: QoS: Get rid of unuseful code and rework CPU latency QoS interface To: Amit Kucheria Cc: "Rafael J. Wysocki" , Linux PM , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 13, 2020 at 8:10 AM Amit Kucheria wrote: > > On Wed, Feb 12, 2020 at 5:09 AM Rafael J. Wysocki wrote: > > > > Hi All, > > > > This series of patches is based on the observation that after commit > > c3082a674f46 ("PM: QoS: Get rid of unused flags") the only global PM QoS class > > in use is PM_QOS_CPU_DMA_LATENCY, but there is still a significant amount of > > code dedicated to the handling of global PM QoS classes in general. That code > > takes up space and adds overhead in vain, so it is better to get rid of it. > > > > Moreover, with that unuseful code removed, the interface for adding QoS > > requests for CPU latency becomes inelegant and confusing, so it is better to > > clean it up. > > > > Patches [01/28-12/28] do the first part described above, which also includes > > some assorted cleanups of the core PM QoS code that doesn't go away. > > > > Patches [13/28-25/28] rework the CPU latency QoS interface (in the classic > > "define stubs, migrate users, change the API proper" manner), patches > > [26-27/28] update the general comments and documentation to match the code > > after the previous changes and the last one makes the CPU latency QoS depend > > on CPU_IDLE (because cpuidle is the only user of its target value today). > > > > The majority of the patches in this series don't change the functionality of > > the code at all (at least not intentionally). > > > > Please refer to the changelogs of individual patches for details. > > Hi Rafael, > > Nice cleanup to the code and docs. > > I've reviewed the series, and briefly tested it by setting latencies > from userspace. Can we not remove the debugfs interface? It is a quick > way to check the global cpu latency clamp on the system from userspace > without setting up tracepoints or writing a program to read > /dev/cpu_dma_latency. Come on. What about in Python? #!/usr/bin/env python import numpy as np if __name__ == '__main__': f = open("/dev/cpu_dma_latency", "r") print(np.fromfile(f, dtype=np.int32, count=1)) f.close() And probably you can do it in at least 20 different ways. :-) Also note that "echo the_debugfs_thing" does the equivalent, but the conversion takes place in the kernel. Is it really a good idea to carry the whole debugfs interface because of that one conversion? > Except for patch 01/28 removing the debugfs interface, please feel to add my > > Reviewed-by: Amit Kucheria > Tested-by: Amit Kucheria Thanks!