• Vineet Gupta's avatar
    ARC: [mm] Lazy D-cache flush (non aliasing VIPT) · eacd0e95
    Vineet Gupta authored
    flush_dcache_page( ) is MM hook to ensure that a page has consistent
    views between kernel and userspace. Thus it is called when
    
    * kernel writes to a page which at some later point could get mapped to
      userspace (so kernel mapping needs to be flushed-n-inv)
    * kernel is about to read from a page with possible userspace mappings
      (so userspace mappings needs to be made coherent with kernel ones)
    
    However for Non aliasing VIPT dcache, any userspace mapping will always
    be congruent to kernel mapping. Thus d-cache need need not be flushed at
    all (or delayed indefinitely).
    
    The only reason it does need to be flushed is when mapping code pages.
    Since icache doesn't snoop dcache, those dirty dcache lines need to be
    written back to memory and icache line invalidated so that icache lines
    fetch will get the right data.
    
    Decent gains on LMBench fork/exec/sh and File I/O micro-benchmarks.
    
    (1) FPGA @ 80 MHZ
    
    Processor, Processes - times in microseconds - smaller is better
    ------------------------------------------------------------------------------
    Host                 OS  Mhz null null      open slct sig  sig  fork exec sh
                                 call  I/O stat clos TCP  inst hndl proc proc proc
    --------- ------------- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
    3.9-rc6-a Linux 3.9.0-r   80 4.79 8.72 66.7 116. 239. 8.39 30.4 4798 14.K 34.K
    3.9-rc6-b Linux 3.9.0-r   80 4.79 8.62 65.4 111. 239. 8.35 29.0 3995 12.K 30.K
    3.9-rc7-c Linux 3.9.0-r   80 4.79 9.00 66.1 106. 239. 8.61 30.4 2858 10.K 24.K
                                                                    ^^^^ ^^^^ ^^^
    
    File & VM system latencies in microseconds - smaller is better
    -------------------------------------------------------------------------------
    Host                 OS   0K File      10K File     Mmap    Prot   Page 100fd
                            Create Delete Create Delete Latency Fault  Fault selct
    --------- ------------- ------ ------ ------ ------ ------- ----- ------- -----
    3.9-rc6-a Linux 3.9.0-r  317.8  204.2 1122.3  375.1 3522.0 4.288     20.7 126.8
    3.9-rc6-b Linux 3.9.0-r  298.7  223.0 1141.6  367.8 3531.0 4.866     20.9 126.4
    3.9-rc7-c Linux 3.9.0-r  278.4  179.2  862.1  339.3 3705.0 3.223     20.3 126.6
                             ^^^^^  ^^^^^  ^^^^^  ^^^^
    
    (2) Customer Silicon @ 500 MHz (166 MHz mem)
    
    ------------------------------------------------------------------------------
    Host                 OS  Mhz null null      open slct sig  sig  fork exec sh
                                 call  I/O stat clos TCP  inst hndl proc proc proc
    --------- ------------- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
    abilis-ba Linux 3.9.0-r  497 0.71 1.38 4.58 12.0 35.5 1.40 3.89 2070 5525 13.K
    abilis-ca Linux 3.9.0-r  497 0.71 1.40 4.61 11.8 35.6 1.37 3.92 1411 4317 10.K
                                                                    ^^^^ ^^^^ ^^^
    Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
    eacd0e95
cacheflush.h 2.59 KB