Messages in this thread |  | | Date | Mon, 2 Apr 2018 16:11:33 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH v5] ANDROID: binder: change down_write to down_read |
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On Mon, Apr 02, 2018 at 02:46:14PM +0800, Ganesh Mahendran wrote: > 2018-04-02 14:34 GMT+08:00 Minchan Kim <minchan@kernel.org>: > > On Fri, Mar 30, 2018 at 12:04:07PM +0200, Greg Kroah-Hartman wrote: > >> On Fri, Mar 30, 2018 at 10:29:21AM +0900, Minchan Kim wrote: > >> > Hi Ganesh, > >> > > >> > On Fri, Mar 30, 2018 at 09:21:55AM +0800, Ganesh Mahendran wrote: > >> > > 2018-03-29 14:54 GMT+08:00 Minchan Kim <minchan@kernel.org>: > >> > > > binder_update_page_range needs down_write of mmap_sem because > >> > > > vm_insert_page need to change vma->vm_flags to VM_MIXEDMAP unless > >> > > > it is set. However, when I profile binder working, it seems > >> > > > every binder buffers should be mapped in advance by binder_mmap. > >> > > > It means we could set VM_MIXEDMAP in binder_mmap time which is > >> > > > already hold a mmap_sem as down_write so binder_update_page_range > >> > > > doesn't need to hold a mmap_sem as down_write. > >> > > > > >> > > > Android suffers from mmap_sem contention so let's reduce mmap_sem > >> > > > down_write. > >> > > > >> > > Hi, Minchan: > >> > > > >> > > It seems there is performance regression of this patch. > >> > > >> > You mean "This patch aims for solving performance regression" not "This patch > >> > makes performance regression"? > >> > > >> > > > >> > > Do you have some test result of android app launch time or binderThroughput? > >> > > >> > Unfortunately, I don't have any number. The goal is to reduce the number of > >> > call mmap_sem as write-side lock because it makes priority inversion of threads > >> > easily and that's one of clear part I spot that we don't need write-side lock. > >> > >> Please always run the binderThroughput tests when making binder changes > >> (there is a binder test suite in the CTS Android tests), as that ensures > >> that you are not causing performance regressions as well as just normal > >> bug regressions :) > > > > Thanks for the information. I didn't notice that such kinds of tests for > > binder. I will keep it in mind. > > > > Today, I have setup the testing for my phone and found testing was very > > fluctuating even without my patch. It might be not good with my test > > skill. I emulated user's behavior with various touch event. With it, I open > > various apps and play with them several times. Before starting the test, > > I did "adb shell stop && adb shell start && echo 3 > /proc/sys/vm/drop_caches" > > > > Such 15% noise was very easy to make it. > > > > Ganesh, How did you measure? What's the stddev? > > Hi, Minchan: > > Sorry for the late response, a little busy these days. :) > > We have our own test tools to measure app launch time, or you can use > android systrace to get the app launch time. We tested your V1 patch: > https://patchwork.kernel.org/patch/10312057/ > and found app lunch time regression.
V1 had a bug with VM_MAYWRITE. Could you confirm it with v5?
Please tell me more detail. What apps are slower compared to old? Every apps are slowed with avg 15%? Then, what's the stddev?
The reason I'm asking is as I mentioned, it would be caused by rw_semaphore implementation and priority of threads which calls binder operation so I guess it would be not deterministic.
When I had an simple experiment, it was very fluctuating as I expected. (the testing enviroment might be not good in my side). If it's real problem on real practice, better fix is not using write_lock of mmap_sem(it's abusing the write-side lock) but should adjust priority, I think. What do you think?
Anyway, before the further discussion, we should confirm the root cause.
> > I will use binderThroghput tool to test the patch today or tomorrow. >
Thanks. I will do.
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