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 <minc...@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, greg k-h
