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authorVineet Gupta <vgupta@synopsys.com>2015-11-17 17:46:48 +0530
committerVineet Gupta <vgupta@synopsys.com>2015-11-17 22:05:30 +0530
commite81b75f7b206d4c44afd20354a66825239490109 (patch)
tree1fefc2f6d91f5183a21b6d0708908b2516a0f6ec /arch/arc
parentb8628f3fe41c999b003c541c078312fcead960d6 (diff)
ARC: remove SYNC from __switch_to()
SYNC in __switch_to() is a historic relic and not needed at all. - In UP context it is obviously useless, why would we want to stall the core for all updates to stack memory of t0 to complete before loading kernel mode callee registers from t1 stack's memory. - In SMP, there could be potential race in which outgoing task could be concurrently picked for running on a different core, thus writes to stack here need to be visible before the reads from stack on other core. Peter confirmed that generic schedular already has needed barriers (by way of rq lock) so there is no need for additional arch barrier. This came up when Noam was trying to replace this SYNC with EZChip specific hardware thread scheduling instruction for their platform support. Link: http://lkml.kernel.org/r/20151102092654.GM17308@twins.programming.kicks-ass.net Cc: Peter Zijlstra <peterz@infradead.org> Cc: linux-kernel@vger.kernel.org Cc: Noam Camus <noamc@ezchip.com> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Diffstat (limited to 'arch/arc')
-rw-r--r--arch/arc/kernel/ctx_sw.c2
-rw-r--r--arch/arc/kernel/ctx_sw_asm.S3
2 files changed, 0 insertions, 5 deletions
diff --git a/arch/arc/kernel/ctx_sw.c b/arch/arc/kernel/ctx_sw.c
index c14a5bea0c76..5d446df2c413 100644
--- a/arch/arc/kernel/ctx_sw.c
+++ b/arch/arc/kernel/ctx_sw.c
@@ -58,8 +58,6 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
"st sp, [r24] \n\t"
#endif
- "sync \n\t"
-
/*
* setup _current_task with incoming tsk.
* optionally, set r25 to that as well
diff --git a/arch/arc/kernel/ctx_sw_asm.S b/arch/arc/kernel/ctx_sw_asm.S
index e248594097e7..e6890b1f8650 100644
--- a/arch/arc/kernel/ctx_sw_asm.S
+++ b/arch/arc/kernel/ctx_sw_asm.S
@@ -44,9 +44,6 @@ __switch_to:
* don't need to do anything special to return it
*/
- /* hardware memory barrier */
- sync
-
/*
* switch to new task, contained in r1
* Temp reg r3 is required to get the ptr to store val