From: Leonardo Bras <leobras@redhat.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Leonardo Bras <leobras@redhat.com>, Guo Ren <guoren@kernel.org>,
linux-kernel@vger.kernel.org, kernel-team@meta.com,
andi.shyti@linux.intel.com, andrzej.hajda@intel.com,
linux-riscv@lists.infradead.org, palmer@dabbelt.com
Subject: Re: [PATCH RFC cmpxchg 8/8] riscv: Emulate one-byte and two-byte cmpxchg
Date: Sat, 11 May 2024 17:44:46 -0300 [thread overview]
Message-ID: <Zj_YvmjROzW6NAog@LeoBras> (raw)
In-Reply-To: <9a84b94c-34ff-4c3a-ab2b-2741a5755db9@paulmck-laptop>
On Sat, May 11, 2024 at 07:54:34AM -0700, Paul E. McKenney wrote:
> On Sat, May 11, 2024 at 02:50:13AM -0400, Guo Ren wrote:
> > On Thu, Apr 04, 2024 at 07:15:40AM -0700, Palmer Dabbelt wrote:
> > > On Mon, 01 Apr 2024 14:39:50 PDT (-0700), paulmck@kernel.org wrote:
> > > > Use the new cmpxchg_emu_u8() and cmpxchg_emu_u16() to emulate one-byte
> > > > and two-byte cmpxchg() on riscv.
> > > >
> > > > [ paulmck: Apply kernel test robot feedback. ]
> > >
> > > I'm not entirely following the thread, but sounds like there's going to be
> > > generic kernel users of this now? Before we'd said "no" to the byte/half
> > > atomic emulation routines beacuse they weren't used, but if it's a generic
> > > thing then I'm find adding them.
> > >
> > > There's a patch set over here
> > > <https://lore.kernel.org/all/20240103163203.72768-2-leobras@redhat.com/>
> > > that implements these more directly using LR/SC. I was sort of on the fence
> > > about just taking it even with no direct users right now, as the byte/half
> > > atomic extension is working its way through the spec process so we'll have
> > > them for real soon. I stopped right there for the last merge window,
> > > though, as I figured it was too late to be messing with the atomics...
> > >
> > > So
> > >
> > > Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
> > F.Y.I Leonardo Bras <leobras@redhat.com>
Hi Guo Ren, thanks for bringing it to my attention.
I am quite excited about the inclusion of my patchset on riscv/cmpxchg, and
I hope it can be useful both to your qspinlock implementation and on Paul's
RCU improvement.
>
> I am carrying this in -rcu, but only for testing purposes, not for
> inclusion into mainline. Not that I know of anyone testing -rcu on
> RISC-V, but still, I wouldn't want to do anything do discourage such
> testing.
>
> The reason that this patch is no longer intended for inclusion is that it
> has been obsoleted by a patch that provides native support for one-byte
> and two-byte cmpxchg() operations. Which is even better! ;-)
>
> Thanx, Paul
Thanks Paul!
Months ago I have reworked cmpxchg and added those 1-byte and 2-byte
{cmp,}xchg asm implementations using lr/sc, as they would be useful to Guo
Ren's qspinlock, and I am thankful that you provided another use case,
because it provides more proof of it's usefulness.
Thanks!
Leo
>
> > > if you guys want to take some sort of tree-wide change to make the byte/half
> > > stuff be required everywhere. We'll eventually end up with arch routines
> > > for the extension, so at that point we might as well also have the more
> > > direct LR/SC flavors.
> > >
> > > If you want I can go review/merge that RISC-V patch set and then it'll have
> > > time to bake for a shared tag you can pick up for all this stuff? No rush
> > > on my end, just LMK.
> > >
> > > > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > > > Cc: Andi Shyti <andi.shyti@linux.intel.com>
> > > > Cc: Andrzej Hajda <andrzej.hajda@intel.com>
> > > > Cc: <linux-riscv@lists.infradead.org>
> > > > ---
> > > > arch/riscv/Kconfig | 1 +
> > > > arch/riscv/include/asm/cmpxchg.h | 25 +++++++++++++++++++++++++
> > > > 2 files changed, 26 insertions(+)
> > > >
> > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > > index be09c8836d56b..4eaf40d0a52ec 100644
> > > > --- a/arch/riscv/Kconfig
> > > > +++ b/arch/riscv/Kconfig
> > > > @@ -44,6 +44,7 @@ config RISCV
> > > > select ARCH_HAS_UBSAN
> > > > select ARCH_HAS_VDSO_DATA
> > > > select ARCH_KEEP_MEMBLOCK if ACPI
> > > > + select ARCH_NEED_CMPXCHG_1_2_EMU
> > > > select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> > > > select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
> > > > select ARCH_STACKWALK
> > > > diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
> > > > index 2fee65cc84432..a5b377481785c 100644
> > > > --- a/arch/riscv/include/asm/cmpxchg.h
> > > > +++ b/arch/riscv/include/asm/cmpxchg.h
> > > > @@ -9,6 +9,7 @@
> > > > #include <linux/bug.h>
> > > >
> > > > #include <asm/fence.h>
> > > > +#include <linux/cmpxchg-emu.h>
> > > >
> > > > #define __xchg_relaxed(ptr, new, size) \
> > > > ({ \
> > > > @@ -170,6 +171,12 @@
> > > > __typeof__(*(ptr)) __ret; \
> > > > register unsigned int __rc; \
> > > > switch (size) { \
> > > > + case 1: \
> > > > + __ret = cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
> > > > + break; \
> > > > + case 2: \
> > > > + break; \
> > > > + __ret = cmpxchg_emu_u16((volatile u16 *)__ptr, __old, __new); \
> > > > case 4: \
> > > > __asm__ __volatile__ ( \
> > > > "0: lr.w %0, %2\n" \
> > > > @@ -214,6 +221,12 @@
> > > > __typeof__(*(ptr)) __ret; \
> > > > register unsigned int __rc; \
> > > > switch (size) { \
> > > > + case 1: \
> > > > + __ret = cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
> > > > + break; \
> > > > + case 2: \
> > > > + break; \
> > > > + __ret = cmpxchg_emu_u16((volatile u16 *)__ptr, __old, __new); \
> > > > case 4: \
> > > > __asm__ __volatile__ ( \
> > > > "0: lr.w %0, %2\n" \
> > > > @@ -260,6 +273,12 @@
> > > > __typeof__(*(ptr)) __ret; \
> > > > register unsigned int __rc; \
> > > > switch (size) { \
> > > > + case 1: \
> > > > + __ret = cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
> > > > + break; \
> > > > + case 2: \
> > > > + break; \
> > > > + __ret = cmpxchg_emu_u16((volatile u16 *)__ptr, __old, __new); \
> > > > case 4: \
> > > > __asm__ __volatile__ ( \
> > > > RISCV_RELEASE_BARRIER \
> > > > @@ -306,6 +325,12 @@
> > > > __typeof__(*(ptr)) __ret; \
> > > > register unsigned int __rc; \
> > > > switch (size) { \
> > > > + case 1: \
> > > > + __ret = cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
> > > > + break; \
> > > > + case 2: \
> > > > + break; \
> > > > + __ret = cmpxchg_emu_u16((volatile u16 *)__ptr, __old, __new); \
> > > > case 4: \
> > > > __asm__ __volatile__ ( \
> > > > "0: lr.w %0, %2\n" \
> > >
>
next prev parent reply other threads:[~2024-05-11 20:45 UTC|newest]
Thread overview: 109+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-01 21:39 [PATCH RFC cmpxchg 0/8] Provide emulation for one- and two-byte cmpxchg() Paul E. McKenney
2024-04-01 21:39 ` [PATCH RFC cmpxchg 1/8] lib: Add one-byte and two-byte cmpxchg() emulation functions Paul E. McKenney
2024-04-02 13:07 ` Marco Elver
2024-04-02 17:15 ` Paul E. McKenney
2024-04-01 21:39 ` [PATCH RFC cmpxchg 2/8] sparc: Emulate one-byte and two-byte cmpxchg Paul E. McKenney
2024-04-01 22:38 ` Al Viro
2024-04-01 23:58 ` Paul E. McKenney
2024-04-02 0:07 ` Al Viro
2024-04-02 3:37 ` Al Viro
2024-04-02 4:11 ` Al Viro
2024-04-02 4:18 ` Paul E. McKenney
2024-04-02 4:28 ` [PATCH 1/8] sparc32: make __cmpxchg_u32() return u32 Al Viro
2024-04-02 4:28 ` [PATCH 2/8] sparc32: make the first argument of __cmpxchg_u64() volatile u64 * Al Viro
2024-04-02 4:28 ` [PATCH 3/8] sparc32: unify __cmpxchg_u{32,64} Al Viro
2024-04-02 7:28 ` Arnd Bergmann
2024-04-02 20:02 ` Paul E. McKenney
2024-04-02 4:28 ` [PATCH 4/8] sparc32: add __cmpxchg_u{8,16}() and teach __cmpxchg() to handle those sizes Al Viro
2024-04-02 4:28 ` [PATCH 5/8] parisc: __cmpxchg_u32(): lift conversion into the callers Al Viro
2024-04-02 4:28 ` [PATCH 6/8] parisc: unify implementations of __cmpxchg_u{8,32,64} Al Viro
2024-04-02 4:28 ` [PATCH 7/8] parisc: add missing export of __cmpxchg_u8() Al Viro
2024-04-02 4:28 ` [PATCH 8/8] parisc: add u16 support to cmpxchg() Al Viro
2024-04-02 20:03 ` [PATCH 1/8] sparc32: make __cmpxchg_u32() return u32 Paul E. McKenney
2024-04-03 22:20 ` Al Viro
2024-04-04 3:09 ` Paul E. McKenney
2024-04-02 4:17 ` [PATCH RFC cmpxchg 2/8] sparc: Emulate one-byte and two-byte cmpxchg Paul E. McKenney
2024-04-01 21:39 ` [PATCH RFC cmpxchg 3/8] ARC: " Paul E. McKenney
2024-04-02 8:14 ` Arnd Bergmann
2024-04-02 17:06 ` Paul E. McKenney
2024-04-02 20:52 ` Paul E. McKenney
2024-04-04 11:57 ` Arnd Bergmann
2024-04-04 14:44 ` Paul E. McKenney
2024-04-04 15:06 ` Arnd Bergmann
2024-04-01 21:39 ` [PATCH RFC cmpxchg 4/8] csky: " Paul E. McKenney
2024-04-01 21:39 ` [PATCH RFC cmpxchg 5/8] sh: " Paul E. McKenney
2024-04-01 21:39 ` [PATCH RFC cmpxchg 6/8] xtensa: " Paul E. McKenney
2024-04-01 21:39 ` [PATCH RFC cmpxchg 7/8] parisc: Emulate " Paul E. McKenney
2024-04-01 21:39 ` [PATCH RFC cmpxchg 8/8] riscv: Emulate one-byte and " Paul E. McKenney
2024-04-04 14:15 ` Palmer Dabbelt
2024-04-04 14:50 ` Paul E. McKenney
2024-05-11 6:50 ` Guo Ren
2024-05-11 14:54 ` Paul E. McKenney
2024-05-11 20:44 ` Leonardo Bras [this message]
2024-04-08 17:47 ` [PATCH RFC cmpxchg 0/8] Provide emulation for one- and two-byte cmpxchg() Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 01/14] sparc32: make __cmpxchg_u32() return u32 Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 02/14] sparc32: make the first argument of __cmpxchg_u64() volatile u64 * Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 03/14] sparc32: unify __cmpxchg_u{32,64} Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 04/14] sparc32: add __cmpxchg_u{8,16}() and teach __cmpxchg() to handle those sizes Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 05/14] parisc: __cmpxchg_u32(): lift conversion into the callers Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 06/14] parisc: unify implementations of __cmpxchg_u{8,32,64} Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 07/14] parisc: add missing export of __cmpxchg_u8() Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 08/14] parisc: add u16 support to cmpxchg() Paul E. McKenney
2024-04-08 20:10 ` Linus Torvalds
2024-04-08 20:53 ` Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 09/14] lib: Add one-byte emulation function Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 10/14] ARC: Emulate one-byte cmpxchg Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 11/14] csky: " Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 12/14] sh: " Paul E. McKenney
2024-04-18 8:04 ` Geert Uytterhoeven
2024-04-08 17:49 ` [PATCH cmpxchg 13/14] xtensa: " Paul E. McKenney
2024-04-18 8:06 ` Geert Uytterhoeven
2024-04-18 23:21 ` Paul E. McKenney
2024-04-19 5:07 ` Yujie Liu
2024-04-19 8:02 ` Geert Uytterhoeven
2024-04-20 14:03 ` Paul E. McKenney
2024-04-08 17:49 ` [PATCH cmpxchg 14/14] riscv: " Paul E. McKenney
2024-04-09 17:35 ` Andrea Parri
2024-04-09 18:08 ` Paul E. McKenney
2024-05-01 22:58 ` [PATCH v2 cmpxchg 0/8] Provide emulation for one--byte cmpxchg() Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 01/13] sparc32: make __cmpxchg_u32() return u32 Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 02/13] sparc32: make the first argument of __cmpxchg_u64() volatile u64 * Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 03/13] sparc32: unify __cmpxchg_u{32,64} Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 04/13] sparc32: add __cmpxchg_u{8,16}() and teach __cmpxchg() to handle those sizes Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 05/13] parisc: __cmpxchg_u32(): lift conversion into the callers Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 06/13] parisc: unify implementations of __cmpxchg_u{8,32,64} Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 07/13] parisc: add missing export of __cmpxchg_u8() Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 08/13] parisc: add u16 support to cmpxchg() Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 09/13] lib: Add one-byte emulation function Paul E. McKenney
2024-05-13 14:44 ` Boqun Feng
2024-05-13 15:41 ` Paul E. McKenney
2024-05-13 15:57 ` Boqun Feng
2024-05-13 21:19 ` Boqun Feng
2024-05-14 14:22 ` Paul E. McKenney
2024-05-14 14:53 ` Boqun Feng
2024-05-14 15:02 ` Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 10/13] ARC: Emulate one-byte cmpxchg Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 11/13] csky: " Paul E. McKenney
2024-05-11 6:42 ` Guo Ren
2024-05-11 14:49 ` Paul E. McKenney
2024-05-01 23:01 ` [PATCH v2 cmpxchg 12/13] sh: " Paul E. McKenney
2024-05-02 4:52 ` John Paul Adrian Glaubitz
2024-05-02 5:06 ` Paul E. McKenney
2024-05-02 5:11 ` John Paul Adrian Glaubitz
2024-05-02 13:33 ` Paul E. McKenney
2024-05-02 20:53 ` Al Viro
2024-05-02 21:01 ` alpha cmpxchg.h (was Re: [PATCH v2 cmpxchg 12/13] sh: Emulate one-byte cmpxchg) Al Viro
2024-05-02 22:16 ` Linus Torvalds
2024-05-02 21:18 ` [PATCH v2 cmpxchg 12/13] sh: Emulate one-byte cmpxchg Paul E. McKenney
2024-05-02 22:07 ` Al Viro
2024-05-02 23:12 ` Paul E. McKenney
2024-05-02 23:24 ` Al Viro
2024-05-02 23:45 ` Paul E. McKenney
2024-05-02 23:32 ` Linus Torvalds
2024-05-03 0:16 ` Paul E. McKenney
2024-05-02 21:50 ` Arnd Bergmann
2024-05-02 5:42 ` D. Jeff Dionne
2024-05-02 11:30 ` Arnd Bergmann
2024-05-01 23:01 ` [PATCH v2 cmpxchg 13/13] xtensa: " Paul E. McKenney
2024-05-02 20:01 ` [PATCH v2 cmpxchg 0/8] Provide emulation for one--byte cmpxchg() Al Viro
2024-05-02 21:20 ` Paul E. McKenney
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