[RFC PATCH] powerpc/book3s64/radix: Upgrade va tlbie to PID tlbie if we cross PMD_SIZE

[Puvichakravarthy Ramachandran]

> 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.kumar at 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;

Additional details on the test environment. This was tested on a 2 Node/8 
socket Power10 system.
The LPAR had 105 cores and the LPAR spanned across all the sockets. 

# perf stat -I 1000 -a -e cycles,instructions -e 
"{cpu/config=0x030008,name=PM_EXEC_STALL/}" -e 
"{cpu/config=0x02E01C,name=PM_EXEC_STALL_TLBIE/}" ./tlbie -i 10 -c 1  -t 1
 Rate of work: = 176 
#           time             counts unit events
     1.029206442         4198594519      cycles  
     1.029206442         2458254252      instructions              # 0.59 
insn per cycle 
     1.029206442         3004031488      PM_EXEC_STALL   
     1.029206442         1798186036      PM_EXEC_STALL_TLBIE   
 Rate of work: = 181 
     2.054288539         4183883450      cycles  
     2.054288539         2472178171      instructions              # 0.59 
insn per cycle 
     2.054288539         3014609313      PM_EXEC_STALL   
     2.054288539         1797851642      PM_EXEC_STALL_TLBIE   
 Rate of work: = 180 
     3.078306883         4171250717      cycles  
     3.078306883         2468341094      instructions              # 0.59 
insn per cycle 
     3.078306883         2993036205      PM_EXEC_STALL   
     3.078306883         1798181890      PM_EXEC_STALL_TLBIE   
.
. 

# cat /sys/kernel/debug/powerpc/tlb_single_page_flush_ceiling
34

# echo 32 > /sys/kernel/debug/powerpc/tlb_single_page_flush_ceiling

# perf stat -I 1000 -a -e cycles,instructions -e 
"{cpu/config=0x030008,name=PM_EXEC_STALL/}" -e 
"{cpu/config=0x02E01C,name=PM_EXEC_STALL_TLBIE/}" ./tlbie -i 10 -c 1  -t 1
 Rate of work: = 313 
#           time             counts unit events
     1.030310506         4206071143      cycles  
     1.030310506         4314716958      instructions              # 1.03 
insn per cycle 
     1.030310506         2157762167      PM_EXEC_STALL   
     1.030310506          110825573      PM_EXEC_STALL_TLBIE   
 Rate of work: = 322 
     2.056034068         4331745630      cycles  
     2.056034068         4531658304      instructions              # 1.05 
insn per cycle 
     2.056034068         2288971361      PM_EXEC_STALL   
     2.056034068          111267927      PM_EXEC_STALL_TLBIE   
 Rate of work: = 321 
     3.081216434         4327050349      cycles  
     3.081216434         4379679508      instructions              # 1.01 
insn per cycle 
     3.081216434         2252602550      PM_EXEC_STALL   
     3.081216434          110974887      PM_EXEC_STALL_TLBIE   
.
.
 

Regards,
Puvichakravarthy Ramachandran