Messages in this thread Patch in this message | | | From | Michael Rodin <> | Subject | [PATCH] arch/x86/entry/vsyscall/vsyscall_gtod.c: remove __read_mostly from vclocks_used | Date | Mon, 4 Jun 2018 19:27:11 +0200 |
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The variable "vclocks_used" doesn't appear to be "read mostly". Measurements of the access frequency with perf stat [1] and perf report show, that approximately half of the accesses to this variable are write accesses and happen in update_vsyscall() in the file arch/x86/entry/vsyscall/vsyscall_gtod.c. The measurements were done with the kernel 4.13.0-43-generic used by ubuntu as well as with the stable kernel 4.16.7 with a custom config. I've used "perf bench sched" and iperf3 as workloads.
This was discovered during my master thesis in the CADOS project [2].
[1] perf stat --all-cpus --group --event="{mem:addr/4:rw:k,mem:addr/4:w:k}" [2] https://www.sra.uni-hannover.de/Research/CADOS/
Signed-off-by: Michael Rodin <michael-git@rodin.online> --- arch/x86/entry/vsyscall/vsyscall_gtod.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/entry/vsyscall/vsyscall_gtod.c b/arch/x86/entry/vsyscall/vsyscall_gtod.c index e1216dd95c04..fc39f701fe4a 100644 --- a/arch/x86/entry/vsyscall/vsyscall_gtod.c +++ b/arch/x86/entry/vsyscall/vsyscall_gtod.c @@ -17,7 +17,7 @@ #include <asm/vgtod.h> #include <asm/vvar.h> -int vclocks_used __read_mostly; +int vclocks_used; DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data); -- 2.14.1
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