aboutsummaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorJohn David Anglin <dave.anglin@bell.net>2014-05-11 18:40:50 -0400
committerHelge Deller <deller@gmx.de>2014-05-15 21:12:26 +0200
commitc776cd89fc705fc8b5c2e5ad906bf5d791620fed (patch)
treec6f26e9791042801f87cd36d87ebb0d527b344b1
parentfef47e2a2e1e75fe50a10f634a80f16808348cc6 (diff)
downloadlinux-c776cd89fc705fc8b5c2e5ad906bf5d791620fed.tar.gz
parisc: Improve LWS-CAS performance
The attached change significantly improves the performance of the LWS-CAS code in syscall.S. This allows a number of packages to build (e.g., zeromq3, gtest and libxs) that previously failed because slow LWS-CAS performance under contention. In particular, interrupts taken while the lock was taken degraded performance significantly. The change does the following: 1) Disables interrupts around the CAS operation, and 2) Changes the loads and stores to use the ordered completer, "o", on PA 2.0. "o" and "ma" with a zero offset are equivalent. The latter is accepted on both PA 1.X and 2.0. The use of ordered loads and stores probably makes no difference on all existing hardware, but it seemed pedantically correct. In particular, the CAS operation must complete before LDCW lock is released. As written before, a processor could reorder the operations. I don't believe the period interrupts are disabled is long enough to significantly increase interrupt latency. For example, the TLB insert code is longer. Worst case is a memory fault in the CAS operation. Signed-off-by: John David Anglin <dave.anglin@bell.net> Cc: stable@vger.kernel.org # 3.13+ Signed-off-by: Helge Deller <deller@gmx.de>
-rw-r--r--arch/parisc/kernel/syscall.S12
1 files changed, 9 insertions, 3 deletions
diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
index a63bb179f79a..838786011037 100644
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -589,10 +589,13 @@ cas_nocontend:
# endif
/* ENABLE_LWS_DEBUG */
+ rsm PSW_SM_I, %r0 /* Disable interrupts */
+ /* COW breaks can cause contention on UP systems */
LDCW 0(%sr2,%r20), %r28 /* Try to acquire the lock */
cmpb,<>,n %r0, %r28, cas_action /* Did we get it? */
cas_wouldblock:
ldo 2(%r0), %r28 /* 2nd case */
+ ssm PSW_SM_I, %r0
b lws_exit /* Contended... */
ldo -EAGAIN(%r0), %r21 /* Spin in userspace */
@@ -619,15 +622,17 @@ cas_action:
stw %r1, 4(%sr2,%r20)
#endif
/* The load and store could fail */
-1: ldw 0(%sr3,%r26), %r28
+1: ldw,ma 0(%sr3,%r26), %r28
sub,<> %r28, %r25, %r0
-2: stw %r24, 0(%sr3,%r26)
+2: stw,ma %r24, 0(%sr3,%r26)
/* Free lock */
- stw %r20, 0(%sr2,%r20)
+ stw,ma %r20, 0(%sr2,%r20)
#if ENABLE_LWS_DEBUG
/* Clear thread register indicator */
stw %r0, 4(%sr2,%r20)
#endif
+ /* Enable interrupts */
+ ssm PSW_SM_I, %r0
/* Return to userspace, set no error */
b lws_exit
copy %r0, %r21
@@ -639,6 +644,7 @@ cas_action:
#if ENABLE_LWS_DEBUG
stw %r0, 4(%sr2,%r20)
#endif
+ ssm PSW_SM_I, %r0
b lws_exit
ldo -EFAULT(%r0),%r21 /* set errno */
nop