kernel.git/arch/mips/include/asm/spinlock.h, branch linux-4.8.y

locking/spinlock, arch: Update and fix spin_unlock_wait() implementations

2016-06-14T09:55:15Z

This patch updates/fixes all spin_unlock_wait() implementations. The update is in semantics; where it previously was only a control dependency, we now upgrade to a full load-acquire to match the store-release from the spin_unlock() we waited on. This ensures that when spin_unlock_wait() returns, we're guaranteed to observe the full critical section we waited on. This fixes a number of spin_unlock_wait() users that (not unreasonably) rely on this. I also fixed a number of ticket lock versions to only wait on the current lock holder, instead of for a full unlock, as this is sufficient. Furthermore; again for ticket locks; I added an smp_rmb() in between the initial ticket load and the spin loop testing the current value because I could not convince myself the address dependency is sufficient, esp. if the loads are of different sizes. I'm more than happy to remove this smp_rmb() again if people are certain the address dependency does indeed work as expected. Note: PPC32 will be fixed independently Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: chris@zankel.net Cc: cmetcalf@mellanox.com Cc: davem@davemloft.net Cc: dhowells@redhat.com Cc: james.hogan@imgtec.com Cc: jejb@parisc-linux.org Cc: linux@armlinux.org.uk Cc: mpe@ellerman.id.au Cc: ralf@linux-mips.org Cc: realmz6@gmail.com Cc: rkuo@codeaurora.org Cc: rth@twiddle.net Cc: schwidefsky@de.ibm.com Cc: tony.luck@intel.com Cc: vgupta@synopsys.com Cc: ysato@users.sourceforge.jp Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

MIPS: Select CONFIG_ARCH_USE_CMPXCHG_LOCKREF for MIPS64

2015-09-03T10:08:01Z

On MIPS64 we have spinlocks that are 32b in size and an efficient cmpxchg64 implementation, so we qualify to make use of cmpxchg backed lockrefs. Select the ARCH_USE_CMPXCHG_LOCKREF Kconfig symbol and provide a trivial implementation of arch_spin_value_unlocked to satisfy the lockref code. Using Linus' simple testcase from http://article.gmane.org/gmane.linux.file-systems/77466 on a dual core system with an in-development MIPS64 CPU running on FPGA I see around an 8% gain: Pre-patch: Total loops: 252698 Total loops: 251482 Total loops: 250806 Total loops: 252885 Total loops: 251666 Post-patch: Total loops: 273728 Total loops: 269932 Total loops: 269341 Total loops: 275004 Total loops: 270208 [ralf@linux-mips.org: Fixed conflict.] Signed-off-by: Paul Burton Cc: linux-mips@linux-mips.org Cc: Steven J. Hill Cc: linux-kernel@vger.kernel.org Cc: Maciej W. Rozycki Cc: Markos Chandras Patchwork: https://patchwork.linux-mips.org/patch/10810/ Signed-off-by: Ralf Baechle

MIPS: spinlock: Adjust arch_spin_lock back-off time

2015-06-24T12:57:46Z

Make it similar to the trylock and R10000_LLSC_WAR cases. Signed-off-by: Markos Chandras Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/9789/ Signed-off-by: Ralf Baechle

MIPS: Replace smp_mb with release barrier function in unlocks.

2015-06-21T19:54:30Z

Repleace smp_mb() in arch_write_unlock() and __clear_bit_unlock() to smp_mb__before_llsc() call which does "release" barrier functionality. It seems like it was missed in commit f252ffd50c97dae87b45f1dbad24f71358ccfbd6 during introduction of "acquire" and "release" semantics. [ralf@linux-mips: The original patch submission was labelled a fix but actually it replaces a barrier with another less restrictive type of barrier so it doesn't fix any ill behaviour but rather squeezes out a tad better performance. Further improvments will be possible once smp_release() has been merged.] Signed-off-by: Leonid Yegoshin Cc: linux-mips@linux-mips.org Cc: benh@kernel.crashing.org Cc: will.deacon@arm.com Cc: linux-kernel@vger.kernel.org Cc: markos.chandras@imgtec.com Cc: macro@linux-mips.org Cc: Steven.Hill@imgtec.com Cc: alexander.h.duyck@redhat.com Cc: davem@davemloft.net Patchwork: https://patchwork.linux-mips.org/patch/10507/ Signed-off-by: Ralf Baechle

MIPS: asm: spinlock: Fix addiu instruction for R10000_LLSC_WAR case

2015-04-10T13:41:46Z

Commit 5753762cbd1c("MIPS: asm: spinlock: Replace "sub" instruction with "addiu") replaced the "sub" instruction with addiu but it did not update the immediate value in the R10000_LLSC_WAR case. Signed-off-by: Markos Chandras Fixes: 5753762cbd1c("MIPS: asm: spinlock: Replace "sub" instruction with "addiu"") Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/9385/ Signed-off-by: Ralf Baechle

MIPS: asm: spinlock: Replace "sub" instruction with "addiu"

2015-02-17T15:37:23Z

"sub $reg, imm" is not a real MIPS instruction. The assembler can replace that with "addi $reg, -imm". However, addi has been removed from R6, so we replace the "sub" instruction with the "addiu" one. Signed-off-by: Markos Chandras

MIPS: asm: Rename GCC_OFF12_ASM to GCC_OFF_SMALL_ASM

2015-02-17T15:37:21Z

The GCC_OFF12_ASM macro is used for 12-bit immediate constrains but we will also use it for 9-bit constrains on MIPS R6 so we rename it to something more appropriate. Cc: Maciej W. Rozycki Signed-off-by: Markos Chandras

MIPS: Fix microMIPS LL/SC immediate offsets

2014-11-24T06:45:36Z

In the microMIPS encoding some memory access instructions have their immediate offset reduced to 12 bits only. That does not match the GCC `R' constraint we use in some places to satisfy the requirement, resulting in build failures like this: {standard input}: Assembler messages: {standard input}:720: Error: macro used $at after ".set noat" {standard input}:720: Warning: macro instruction expanded into multiple instructions Fix the problem by defining a macro, `GCC_OFF12_ASM', that expands to the right constraint depending on whether microMIPS or standard MIPS code is produced. Also apply the fix to where `m' is used as in the worst case this change does nothing, e.g. where the pointer was already in a register such as a function argument and no further offset was requested, and in the best case it avoids an extraneous sequence of up to two instructions to load the high 20 bits of the address in the LL/SC loop. This reduces the risk of lock contention that is the higher the more instructions there are in the critical section between LL and SC. Strictly speaking we could just bulk-replace `R' with `ZC' as the latter constraint adjusts automatically depending on the ISA selected. However it was only introduced with GCC 4.9 and we keep supporing older compilers for the standard MIPS configuration, hence the slightly more complicated approach I chose. The choice of a zero-argument function-like rather than an object-like macro was made so that it does not look like a function call taking the C expression used for the constraint as an argument. This is so as not to confuse the reader or formatting checkers like `checkpatch.pl' and follows previous practice. Signed-off-by: Maciej W. Rozycki Signed-off-by: Steven J. Hill Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/8482/ Signed-off-by: Ralf Baechle

MIPS: Remove redundant instructions from arch_spin_{,try}lock.

2013-04-26T15:18:24Z

We were doing: SRL $r,$?,16 ANDI $r,$r,0xffff The logical right shift by 16 leaves the upper 16 bits clear, so the subsequent masking out of those bits is redundant, and can safely be removed. Signed-off-by: David Daney Cc: linux-mips@linux-mips.org Signed-off-by: Ralf Baechle

MIPS: Remove further use of .subsection

2013-04-11T13:39:52Z

7837314d141c661c70bc13c5050694413ecfe14a [MIPS: Get rid of branches to .subsections] removed most uses of .subsection] removed most uses of .subsection in inline assembler code. It left the instances in spinlock.h alone because we knew their use was in fairly small files where .subsection use was fine but of course this was a fragile assumption. LTO breaks this assumption resulting in build errors due to exceeded branch range, so remove further instances of .subsection. The two functions that still use .macro don't currently cause issues however this use is still fragile. Signed-off-by: Ralf Baechle