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McKenney" , Boqun Feng , linux-kernel , linux-api , Thomas Gleixner , Andy Lutomirski , Dave Watson , Paul Turner , Andrew Morton , Russell King , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Will Deacon , Michael Kerrisk , Joel Fernandes Message-ID: <1006597066.825.1539789100381.JavaMail.zimbra@efficios.com> In-Reply-To: <20181017071931.GA18379@linux.vnet.ibm.com> References: <20181010191936.7495-1-mathieu.desnoyers@efficios.com> <20181010191936.7495-7-mathieu.desnoyers@efficios.com> <20181017071931.GA18379@linux.vnet.ibm.com> Subject: Re: [RFC PATCH for 4.21 06/16] cpu_opv: Provide cpu_opv system call (v8) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.10_GA_3039 (ZimbraWebClient - FF52 (Linux)/8.8.10_GA_3041) Thread-Topic: cpu_opv: Provide cpu_opv system call (v8) Thread-Index: 7qW2lzGCTO+IxFmqU0Kf5LalV47JZQ== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Oct 17, 2018, at 3:19 AM, Srikar Dronamraju srikar@linux.vnet.ibm.com wrote: > Hi Mathieu, > >> +static int do_cpu_opv(struct cpu_op *cpuop, int cpuopcnt, >> + struct cpu_opv_vaddr *vaddr_ptrs, int cpu) >> +{ >> + struct mm_struct *mm = current->mm; >> + int ret; >> + >> +retry: >> + if (cpu != raw_smp_processor_id()) { >> + ret = push_task_to_cpu(current, cpu); >> + if (ret) >> + goto check_online; >> + } >> + down_read(&mm->mmap_sem); >> + ret = vaddr_ptrs_check(vaddr_ptrs); >> + if (ret) >> + goto end; >> + preempt_disable(); >> + if (cpu != smp_processor_id()) { >> + preempt_enable(); >> + up_read(&mm->mmap_sem); >> + goto retry; >> + } > > If we have a higher priority task/s either pinned to the cpu, dont we end up > in busy-looping till the task exits/sleeps? You're right! How about we ditch the thread migration altogether, and simply perform the cpu_opv operations in a IPI handler ? This is possible now that cpu_opv uses a temporary vmap() rather than try to touch the user-space page through the current thread's page table. Thoughts ? Thanks, Mathieu > >> + ret = __do_cpu_opv(cpuop, cpuopcnt); >> + preempt_enable(); >> +end: >> + up_read(&mm->mmap_sem); >> + return ret; >> + >> +check_online: >> + /* >> + * push_task_to_cpu() returns -EINVAL if the requested cpu is not part >> + * of the current thread's cpus_allowed mask. >> + */ >> + if (ret == -EINVAL) >> + return ret; >> + get_online_cpus(); >> + if (cpu_online(cpu)) { >> + put_online_cpus(); >> + goto retry; > > + } -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com