Re: [PATCH] arm64: Skip apply SSBS call for non SSBS system

From: Gaurav Kohli
Date: Wed Aug 12 2020 - 10:17:13 EST

On 8/12/2020 7:00 PM, Will Deacon wrote:
On Tue, Aug 04, 2020 at 07:44:42PM +0530, Gaurav Kohli wrote:
In a system where no cpu's implement SSBS, for
them no need to set pstate. This might help to save
few cpu cycles during context switch.

Signed-off-by: Gaurav Kohli <gkohli@xxxxxxxxxxxxxx>

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 6089638..79f80f1 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -477,6 +477,13 @@ static void ssbs_thread_switch(struct task_struct *next)
struct pt_regs *regs = task_pt_regs(next);
+ * For Targets which don't have SSBS support, they
+ * can return from here.
+ */
+ return;

Does this actually make a measurable difference?


Hi Will,

While doing code review between older kernel and latest kernel for context switch case, there i have found this and thought it is good to have for non-ssbs system to return early(as this might improve).

Please let me know if you want to run some tests.