From: Guo Ren <guoren@kernel.org> To: Arnd Bergmann <arnd@arndb.de> Cc: Waiman Long <longman@redhat.com>, Palmer Dabbelt <palmer@rivosinc.com>, Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>, Boqun Feng <boqun.feng@gmail.com>, linux-riscv <linux-riscv@lists.infradead.org>, linux-arch <linux-arch@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Guo Ren <guoren@linux.alibaba.com>, Peter Zijlstra <peterz@infradead.org> Subject: Re: [PATCH V7 4/5] asm-generic: spinlock: Add combo spinlock (ticket & queued) Date: Wed, 29 Jun 2022 16:24:03 +0800 [thread overview] Message-ID: <CAJF2gTTtKiMZJLWBEcRz-4CmNojH0cOgpUYGupLyCXXFjQD_FQ@mail.gmail.com> (raw) In-Reply-To: <CAK8P3a2jQ+UQ54=QcpyVt91vXRyZrvUtOygFYOHWTBzse3q3rg@mail.gmail.com> On Wed, Jun 29, 2022 at 3:09 PM Arnd Bergmann <arnd@arndb.de> wrote: > > On Wed, Jun 29, 2022 at 3:34 AM Waiman Long <longman@redhat.com> wrote: > > On 6/28/22 21:17, Guo Ren wrote: > > > On Wed, Jun 29, 2022 at 2:13 AM Waiman Long <longman@redhat.com> wrote: > > >> On 6/28/22 04:17, guoren@kernel.org wrote: > > >> > > >> So the current config setting determines if qspinlock will be used, not > > >> some boot time parameter that user needs to specify. This patch will > > >> just add useless code to lock/unlock sites. I don't see any benefit of > > >> doing that. > > > This is a startup patch for riscv. next, we could let vendors make choices. > > > I'm not sure they like cmdline or vendor-specific errata style. > > > > > > Eventually, we would let one riscv Image support all machines, some > > > use ticket-lock, and some use qspinlock. > > > > OK. Maybe you can postpone this combo spinlock until there is a good use > > case for it. Upstream usually don't accept patches that have no good use > > case yet. > > I think the usecase on risc-v is this: there are cases where the qspinlock > is preferred for performance reasons, but there are also CPU cores on > which it is not safe to use. risc-v like most modern architectures has a > strict rule about being able to build kernels that work on all machines, > so without something like this, it would not be able to use qspinlock at all. > > On the other hand, I don't really like the idea of putting the static-key > wrapper into the asm-generic header. Especially the ticket spinlock > implementation should be simple and not depend on jump labels. If CONFIG_ARCH_USE_QUEUED_SPINLOCKS is not enabled, the patch still will keep the ticket-lock simple without jump labels. > > From looking at the header file dependencies on arm64, I know that > putting jump labels into core infrastructure like the arch_spin_lock() > makes a big mess of indirect includes and measurably slows down > the kernel build. arm64 needn't combo spinlock, it could use pure qspinlock with keeping current header files included. > > I think this can still be done in the riscv asm/spinlock.h header with > minimal impact on the asm-generic file if the riscv maintainers see > a significant enough advantage, but I don't want it in the common code. Yes, it could. I agree with using combo spinlock only with riscv. > > Arnd -- Best Regards Guo Ren ML: https://lore.kernel.org/linux-csky/
WARNING: multiple messages have this Message-ID (diff)
From: Guo Ren <guoren@kernel.org> To: Arnd Bergmann <arnd@arndb.de> Cc: Waiman Long <longman@redhat.com>, Palmer Dabbelt <palmer@rivosinc.com>, Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>, Boqun Feng <boqun.feng@gmail.com>, linux-riscv <linux-riscv@lists.infradead.org>, linux-arch <linux-arch@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Guo Ren <guoren@linux.alibaba.com>, Peter Zijlstra <peterz@infradead.org> Subject: Re: [PATCH V7 4/5] asm-generic: spinlock: Add combo spinlock (ticket & queued) Date: Wed, 29 Jun 2022 16:24:03 +0800 [thread overview] Message-ID: <CAJF2gTTtKiMZJLWBEcRz-4CmNojH0cOgpUYGupLyCXXFjQD_FQ@mail.gmail.com> (raw) In-Reply-To: <CAK8P3a2jQ+UQ54=QcpyVt91vXRyZrvUtOygFYOHWTBzse3q3rg@mail.gmail.com> On Wed, Jun 29, 2022 at 3:09 PM Arnd Bergmann <arnd@arndb.de> wrote: > > On Wed, Jun 29, 2022 at 3:34 AM Waiman Long <longman@redhat.com> wrote: > > On 6/28/22 21:17, Guo Ren wrote: > > > On Wed, Jun 29, 2022 at 2:13 AM Waiman Long <longman@redhat.com> wrote: > > >> On 6/28/22 04:17, guoren@kernel.org wrote: > > >> > > >> So the current config setting determines if qspinlock will be used, not > > >> some boot time parameter that user needs to specify. This patch will > > >> just add useless code to lock/unlock sites. I don't see any benefit of > > >> doing that. > > > This is a startup patch for riscv. next, we could let vendors make choices. > > > I'm not sure they like cmdline or vendor-specific errata style. > > > > > > Eventually, we would let one riscv Image support all machines, some > > > use ticket-lock, and some use qspinlock. > > > > OK. Maybe you can postpone this combo spinlock until there is a good use > > case for it. Upstream usually don't accept patches that have no good use > > case yet. > > I think the usecase on risc-v is this: there are cases where the qspinlock > is preferred for performance reasons, but there are also CPU cores on > which it is not safe to use. risc-v like most modern architectures has a > strict rule about being able to build kernels that work on all machines, > so without something like this, it would not be able to use qspinlock at all. > > On the other hand, I don't really like the idea of putting the static-key > wrapper into the asm-generic header. Especially the ticket spinlock > implementation should be simple and not depend on jump labels. If CONFIG_ARCH_USE_QUEUED_SPINLOCKS is not enabled, the patch still will keep the ticket-lock simple without jump labels. > > From looking at the header file dependencies on arm64, I know that > putting jump labels into core infrastructure like the arch_spin_lock() > makes a big mess of indirect includes and measurably slows down > the kernel build. arm64 needn't combo spinlock, it could use pure qspinlock with keeping current header files included. > > I think this can still be done in the riscv asm/spinlock.h header with > minimal impact on the asm-generic file if the riscv maintainers see > a significant enough advantage, but I don't want it in the common code. Yes, it could. I agree with using combo spinlock only with riscv. > > Arnd -- Best Regards Guo Ren ML: https://lore.kernel.org/linux-csky/ _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2022-06-29 8:24 UTC|newest] Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-06-28 8:17 [PATCH V7 0/5] riscv: Add qspinlock support with combo style guoren 2022-06-28 8:17 ` guoren 2022-06-28 8:17 ` [PATCH V7 1/5] asm-generic: ticket-lock: Remove unnecessary atomic_read guoren 2022-06-28 8:17 ` guoren 2022-06-28 18:05 ` Waiman Long 2022-06-28 18:05 ` Waiman Long 2022-06-29 2:12 ` Guo Ren 2022-06-29 2:12 ` Guo Ren 2022-06-29 8:27 ` David Laight 2022-06-29 8:27 ` David Laight 2022-07-01 15:18 ` Guo Ren 2022-07-01 15:18 ` Guo Ren 2022-07-04 9:52 ` Peter Zijlstra 2022-07-04 9:52 ` Peter Zijlstra 2022-07-04 11:10 ` Guo Ren 2022-07-04 11:10 ` Guo Ren 2022-06-28 8:17 ` [PATCH V7 2/5] asm-generic: ticket-lock: Use the same struct definitions with qspinlock guoren 2022-06-28 8:17 ` guoren 2022-06-28 8:17 ` [PATCH V7 3/5] asm-generic: ticket-lock: Move into ticket_spinlock.h guoren 2022-06-28 8:17 ` guoren 2022-06-28 8:17 ` [PATCH V7 4/5] asm-generic: spinlock: Add combo spinlock (ticket & queued) guoren 2022-06-28 8:17 ` guoren 2022-06-28 18:13 ` Waiman Long 2022-06-28 18:13 ` Waiman Long 2022-06-29 1:17 ` Guo Ren 2022-06-29 1:17 ` Guo Ren 2022-06-29 1:34 ` Waiman Long 2022-06-29 1:34 ` Waiman Long 2022-06-29 2:29 ` Guo Ren 2022-06-29 2:29 ` Guo Ren 2022-06-29 7:08 ` Arnd Bergmann 2022-06-29 7:08 ` Arnd Bergmann 2022-06-29 8:24 ` Guo Ren [this message] 2022-06-29 8:24 ` Guo Ren 2022-06-29 8:29 ` Arnd Bergmann 2022-06-29 8:29 ` Arnd Bergmann 2022-07-01 12:18 ` Guo Ren 2022-07-01 12:18 ` Guo Ren 2022-06-29 12:53 ` Waiman Long 2022-06-29 12:53 ` Waiman Long 2022-07-04 9:57 ` Peter Zijlstra 2022-07-04 9:57 ` Peter Zijlstra 2022-07-04 13:13 ` Guo Ren 2022-07-04 13:13 ` Guo Ren 2022-07-04 13:45 ` Peter Zijlstra 2022-07-04 13:45 ` Peter Zijlstra 2022-06-28 8:17 ` [PATCH V7 5/5] riscv: Add qspinlock support guoren 2022-06-28 8:17 ` guoren
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