Re: [BProc] vmadump performance

[Grant T. <gt...@sw...>]

>>>>> Erik Arjan Hendriks <er...@he...> writes:
>>  - Removing seemingly uneeded icache flushes for non-executable pages
>>    in load_map makes no difference, time-wise, on my platform.  This

> That's good.  I don't find it surprising though since most of the
> addresses involved in the flush aren't going to be in the icache

OK, I lied.  Evidently that experiment was done with the wrong kernel
or something.  In fact it's like 5X faster, as cache fluses are fairly
expensive on my (SMP) platform.  Profile below.

So you definitely want to stick an if around the flush_icache_range
call for the benefit of those of us with expensive ipi cache
nastiness:

      if (mmap_prot & PROT_EXEC) {
        flush_icache_range(page.start, page.start + PAGE_SIZE);
      }

I also observe in my profile that the read's memcpy ("both_aligned" in
my profile) and the fault's memzero ("sb1_clear_page") each take
nearly half the time.  I'm going to bodge together some way to skip
the page clear for this case; we already know we're overwriting the
whole page, so this should be OK as long as it gets carefully zeroed
on error.  It'll be pretty ugly, though, so I suspect you won't
actually want it.


With needless flushes:

   218 smp_call_function                          0.5240
    34 both_aligned                               0.3148
    24 local_sb1_flush_icache_range               0.1200
    10 sb1_flush_icache_range_ipi                 0.2500
     8 sb1_clear_page                             0.2000
     5 cleanup_both_aligned                       0.0781
     4 kunmap_high                                0.0135
     4 do_anonymous_page                          0.0069
     3 kmap_high                                  0.0056
     2 zap_page_range                             0.0017
     2 sb1_copy_page                              0.0167
     2 pte_alloc                                  0.0047
     2 do_shmem_file_read                         0.0054

Without needless flushes:

    34 both_aligned                               0.3148
    12 sb1_clear_page                             0.3000
     7 cleanup_both_aligned                       0.1094
     4 sb1_sanitize_tlb                           0.0312
     2 kmap_high                                  0.0037
     2 __free_pages_ok                            0.0017
     1 zap_page_range                             0.0009
     1 smp_call_function                          0.0024
     1 shmem_getpage_locked                       0.0007
     1 shmem_getpage                              0.0025
     1 shmem_file_read                            0.0078
     1 sb1_copy_page                              0.0083
     1 sb1___flush_cache_all_ipi                  0.0078


--
Grant Taylor - x285 - http://pasta/~gtaylor/
Starent Networks - +1.978.851.1185