Re: Deadlock on the mm->mmap_sem

[David Howells]

Andrea Arcangeli <[e-mail]> wrote:
> On Wed, Sep 19, 2001 at 07:26:33PM +0100, David Howells wrote:
> > > if we go generic then I strongly recommend my version of the generic
> > > semaphores is _much_ faster (and cleaner) than this one
> >
> > Not so:-) Your patch, Andrea, grabs the spinlock far more than is necessary.
> 
> then why your microbenchmarks says my version is much faster?

They don't:

[my rwsem-unfair-2.diff patch]
#rds #wrs time :  rd granted [spread]  wr granted [spread]
==== ==== =====   ===================  ===================
   1    0   10s:    25384639 [0.008%]           0 [0.000%]
   2    0   10s:     8007388 [0.013%]           0 [0.000%]
   4    0   10s:     8004833 [0.007%]           0 [0.000%]
   0    1   10s:           0 [0.000%]    25717288 [0.009%]
   0    4   10s:           0 [0.000%]     2817293 [2.323%]
   4    2   10s:    12742523 [0.008%]         114 [5.394%]
  30    1   10s:    12739163 [0.002%]          92 [1.739%]
  30   15   50s:    63733591 [0.003%]         286 [2.711%]

[Andrea's 00_rwsem-19 patch]
#rds #wrs time :  rd granted [spread]  wr granted [spread]
==== ==== =====   ===================  ===================
   1    0   10s:    24577938 [0.003%]           0 [0.000%]
   2    0   10s:     5631224 [0.016%]           0 [0.000%]
   4    0   10s:     5633280 [0.009%]           0 [0.000%]
   0    1   10s:           0 [0.000%]    24572785 [0.007%]
   0    4   10s:           0 [0.000%]     3444786 [0.091%]
   4    2   10s:     8036291 [0.008%]         122 [4.918%]
  30    1   10s:     8036490 [0.006%]          89 [1.253%]
  30   15   50s:    40200472 [0.001%]         265 [2.717%]

[Unpatched kernel]
#rds #wrs time :  rd granted [spread]  wr granted [spread]
==== ==== =====   ===================  ===================
   1    0   10s:    30118903 [0.008%]           0 [0.000%]
   2    0   10s:    12543737 [0.007%]           0 [0.000%]
   4    0   10s:    12543731 [0.006%]           0 [0.000%]
   0    1   10s:           0 [0.000%]    28408147 [0.008%]
   0    4   10s:           0 [0.000%]     1554495 [0.172%]
   4    2   10s:     1119656 [0.076%]      560020 [0.077%]
  30    1   10s:     5361923 [0.024%]       55787 [0.012%]
  30   15   50s:     5322473 [0.049%]     2661621 [0.050%]

David