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SubjectRe: How to calculate instruction executed for function
Date

________________________________________
From: Pankaj Suryawanshi
Sent: 03 April 2019 19:50
To: linux-mm@kvack.org; linux-kernel@vger.kernel.org
Subject: How to calculate instruction executed for function

Hello,

How to calculate instruction executed for function ?

For eg.

I need to calculate instruction executed for CMA_ALLOC function.
How many instruction executed for cma_alloc ?


CMA_ALLOC :

for 1 cma_alloc success call there will around 75 instruction is executed, excluding jump, mutex,error case and debug info instruction.

below are mandatory jump calls that are required for successful allocations.

cma_bitmap_aligned_mask
cma_bitmap_aligned_offset
cma_bitmap_maxno
cma_bitmap_pages_to_bits
bitmap_find_next_zero_area_off -> find_next_zero_bit -> find_next_bit
bitmap_set
alloc_contig_range -> start_isolate_page_range
__alloc_contig_migrate_range -> isolate_migratepages_range -> reclaim_clean_pages_from_list -> shrink_page_list -> migrate_pages


So lets say

cma_bitmap_aligned_mask = 1 instrs
cma_bitmap_aligned_offset = 1 instrs
cma_bitmap_maxno = 1 instrs
cma_bitmap_pages_to_bits = 1 instrs

bitmap_find_next_zero_area_off -> find_next_zero_bit -> find_next_bit = 3 instrs
bitmap_set = 1 instrs
alloc_contig_range -> start_isolate_page_range =

has_unmovable_pages = 1 instrs
get_pfnblock_flags_mask = 1 instrs
set_pageblock_migratetype = 1 instrs
move_freepages_block = 1 instrn
__mod_zone_page_state = 1 instrs store info in vmstat
unset_migratetype_isolate = 1 instrs

__alloc_contig_migrate_range -> isolate_migratepages_range -> reclaim_clean_pages_from_list -> shrink_page_list -> migrate_pages


isolate_migratepages_range = 3 instrs
reclaim_clean_pages_from_list = 2 instrs
migrate_pages = 1 instrs

--------------------------------------------------------------
Total = around 20 instrs per page

20 ns per page on 1ghz processor is minimum excluding any overheads like mutex, variables, failure/error case,debug/prints.

I roughly calculated this.
Is it Correct ?


Any help would be appreciated.

Regards,
Pankaj
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