> With shared mapping, even though we are unmapping a large range, the
kernel
> will force a TLB flush with ptl lock held to avoid the race mentioned in
> commit 1cf35d47712d ("mm: split 'tlb_flush_mmu()' into tlb flushing and
memory freeing parts")
> This results in the kernel issuing a high number of TLB flushes even for
a large
> range. This can be improved by making sure the kernel switch to pid
based flush if the
> kernel is unmapping a 2M range.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
> ---
> arch/powerpc/mm/book3s64/radix_tlb.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c
b/arch/powerpc/mm/book3s64/radix_tlb.c
> index aefc100d79a7..21d0f098e43b 100644
> --- a/arch/powerpc/mm/book3s64/radix_tlb.c
> +++ b/arch/powerpc/mm/book3s64/radix_tlb.c
> @@ -1106,7 +1106,7 @@ EXPORT_SYMBOL(radix__flush_tlb_kernel_range);
> * invalidating a full PID, so it has a far lower threshold to change
from
> * individual page flushes to full-pid flushes.
> */
> -static unsigned long tlb_single_page_flush_ceiling __read_mostly = 33;
> +static unsigned long tlb_single_page_flush_ceiling __read_mostly = 32;
> static unsigned long tlb_local_single_page_flush_ceiling __read_mostly
= POWER9_TLB_SETS_RADIX * 2;
>
> static inline void __radix__flush_tlb_range(struct mm_struct *mm,
> @@ -1133,7 +1133,7 @@ static inline void __radix__flush_tlb_range(struct
mm_struct *mm,
> if (fullmm)
> flush_pid = true;
> else if (type == FLUSH_TYPE_GLOBAL)
> - flush_pid = nr_pages > tlb_single_page_flush_ceiling;
> + flush_pid = nr_pages >= tlb_single_page_flush_ceiling;
> else
> flush_pid = nr_pages >
tlb_local_single_page_flush_ceiling;
I evaluated the patches from Aneesh with a micro benchmark which does
shmat, shmdt of 256 MB segment.
Higher the rate of work, better the performance. With a value of 32, we
match the performance of
GTSE=off. This was evaluated on SLES15 SP3 kernel.
# cat /sys/kernel/debug/powerpc/tlb_single_page_flush_ceiling
32
# perf stat -I 1000 -a -e powerpc:tlbie,r30058 ./tlbie -i 5 -c 1 t 1
Rate of work: = 311
# time counts unit events
1.013131404 50939 powerpc:tlbie
1.013131404 50658 r30058
Rate of work: = 318
2.026957019 51520 powerpc:tlbie
2.026957019 51481 r30058
Rate of work: = 318
3.038884431 51485 powerpc:tlbie
3.038884431 51461 r30058
Rate of work: = 318
4.051483926 51485 powerpc:tlbie
4.051483926 51520 r30058
Rate of work: = 318
5.063635713 48577 powerpc:tlbie
5.063635713 48347 r30058
# echo 34 > /sys/kernel/debug/powerpc/tlb_single_page_flush_ceiling
# perf stat -I 1000 -a -e powerpc:tlbie,r30058 ./tlbie -i 5 -c 1 t 1
Rate of work: = 174
# time counts unit events
1.012672696 721471 powerpc:tlbie
1.012672696 726491 r30058
Rate of work: = 177
2.026348661 737460 powerpc:tlbie
2.026348661 736138 r30058
Rate of work: = 178
3.037932122 737460 powerpc:tlbie
3.037932122 737460 r30058
Rate of work: = 178
4.050198819 737044 powerpc:tlbie
4.050198819 737460 r30058
Rate of work: = 177
5.062400776 692832 powerpc:tlbie
5.062400776 688319 r30058
Regards,
Puvichakravarthy Ramachandran
