module: unify absolute krctab definitions for 32-bit and 64-bit - net-next.git - net-next plumbings

summary refs log tree commit diff

path: root/sound/soc/intel/skylake

diff options

author	Ard Biesheuvel <ard.biesheuvel@linaro.org>	2017-02-03 09:54:07 +0000
committer	Linus Torvalds <torvalds@linux-foundation.org>	2017-02-03 08:28:25 -0800
commit	4b9eee96fcb361a5e16a8d2619825e8a048f81f7 (patch)
tree	1347fe88fba35018e2d9f14be79a7feb29e75151 /sound/soc/intel/skylake
parent	71810db27c1c853b335675bee335d893bc3d324b (diff)

module: unify absolute krctab definitions for 32-bit and 64-bit

The previous patch introduced a separate inline asm version of the krcrctab declaration template for use with 64-bit architectures, which cannot refer to ELF symbols using 32-bit quantities. This declaration should be equivalent to the C one for 32-bit architectures, but just in case - unify them in a separate patch, which can simply be dropped if it turns out to break anything. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Diffstat (limited to 'sound/soc/intel/skylake')

0 files changed, 0 insertions, 0 deletions

, and look at the other bits of the result. However, an even simpler model is to just use a regular atomic "and" to clear the lock bit, and then the sign bit in eflags will indicate the resulting state of the unrelated bit #7. So by moving the PageWaiters bit up to bit #7, we can atomically clear the lock bit and test the waiters bit on x86 too. And architectures with LL/SC (which is all the usual RISC suspects), the particular bit doesn't matter, so they are fine with this approach too. This avoids the extra access to the same atomic word, and thus avoids the costly stall at page unlock time. The only downside is that the interface ends up being a bit odd and specialized: clear a bit in a byte, and test the sign bit. Nick doesn't love the resulting name of the new primitive, but I'd rather make the name be descriptive and very clear about the limitation imposed by trying to work across all relevant architectures than make it be some generic thing that doesn't make the odd semantics explicit. So this introduces the new architecture primitive clear_bit_unlock_is_negative_byte(); and adds the trivial implementation for x86. We have a generic non-optimized fallback (that just does a "clear_bit()"+"test_bit(7)" combination) which can be overridden by any architecture that can do better. According to Nick, Power has the same hickup x86 has, for example, but some other architectures may not even care. All these optimizations mean that my page locking stress-test (which is just executing a lot of small short-lived shell scripts: "make test" in the git source tree) no longer makes our page locking look horribly bad. Before all these optimizations, just the unlock_page() costs were just over 3% of all CPU overhead on "make test". After this, it's down to 0.66%, so just a quarter of the cost it used to be. (The difference on NUMA is bigger, but there this micro-optimization is likely less noticeable, since the big issue on NUMA was not the accesses to 'struct page', but the waitqueue accesses that were already removed by Nick's earlier commit). Acked-by: Nick Piggin <npiggin@gmail.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Bob Peterson <rpeterso@redhat.com> Cc: Steven Whitehouse <swhiteho@redhat.com> Cc: Andrew Lutomirski <luto@kernel.org> Cc: Andreas Gruenbacher <agruenba@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Mel Gorman <mgorman@techsingularity.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Diffstat (limited to 'sound/soc')