1. 13 Feb, 2012 1 commit
    • Shaohua Li's avatar
      readahead: fix pipeline break caused by block plug · 76af79f3
      Shaohua Li authored
      commit 3deaa719 upstream.
      
      Herbert Poetzl reported a performance regression since 2.6.39.  The test
      is a simple dd read, but with big block size.  The reason is:
      
      T1: ra (A, A+128k), (A+128k, A+256k)
      T2: lock_page for page A, submit the 256k
      T3: hit page A+128K, ra (A+256k, A+384). the range isn't submitted
      because of plug and there isn't any lock_page till we hit page A+256k
      because all pages from A to A+256k is in memory
      T4: hit page A+256k, ra (A+384, A+ 512). Because of plug, the range isn't
      submitted again.
      T5: lock_page A+256k, so (A+256k, A+512k) will be submitted. The task is
      waitting for (A+256k, A+512k) finish.
      
      There is no request to disk in T3 and T4, so readahead pipeline breaks.
      
      We really don't need block plug for generic_file_aio_read() for buffered
      I/O.  The readahead already has plug and has fine grained control when I/O
      should be submitted.  Deleting plug for buffered I/O fixes the regression.
      
      One side effect is plug makes the request size 256k, the size is 128k
      without it.  This is because default ra size is 128k and not a reason we
      need plug here.
      
      Vivek said:
      
      : We submit some readahead IO to device request queue but because of nested
      : plug, queue never gets unplugged.  When read logic reaches a page which is
      : not in page cache, it waits for page to be read from the disk
      : (lock_page_killable()) and that time we flush the plug list.
      :
      : So effectively read ahead logic is kind of broken in parts because of
      : nested plugging.  Removing top level plug (generic_file_aio_read()) for
      : buffered reads, will allow unplugging queue earlier for readahead.
      Signed-off-by: default avatarShaohua Li <shaohua.li@intel.com>
      Signed-off-by: default avatarWu Fengguang <fengguang.wu@intel.com>
      Reported-by: default avatarHerbert Poetzl <herbert@13thfloor.at>
      Tested-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
      Cc: Christoph Hellwig <hch@infradead.org>
      Cc: Jens Axboe <axboe@kernel.dk>
      Cc: Vivek Goyal <vgoyal@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      76af79f3
  2. 06 Feb, 2012 2 commits
    • Greg Kroah-Hartman's avatar
      Linux 3.2.5 · 61339713
      Greg Kroah-Hartman authored
      61339713
    • Matthew Garrett's avatar
      PCI: Rework ASPM disable code · 2dcce0a3
      Matthew Garrett authored
      commit 3c076351 upstream.
      
      Right now we forcibly clear ASPM state on all devices if the BIOS indicates
      that the feature isn't supported. Based on the Microsoft presentation
      "PCI Express In Depth for Windows Vista and Beyond", I'm starting to think
      that this may be an error. The implication is that unless the platform
      grants full control via _OSC, Windows will not touch any PCIe features -
      including ASPM. In that case clearing ASPM state would be an error unless
      the platform has granted us that control.
      
      This patch reworks the ASPM disabling code such that the actual clearing
      of state is triggered by a successful handoff of PCIe control to the OS.
      The general ASPM code undergoes some changes in order to ensure that the
      ability to clear the bits isn't overridden by ASPM having already been
      disabled. Further, this theoretically now allows for situations where
      only a subset of PCIe roots hand over control, leaving the others in the
      BIOS state.
      
      It's difficult to know for sure that this is the right thing to do -
      there's zero public documentation on the interaction between all of these
      components. But enough vendors enable ASPM on platforms and then set this
      bit that it seems likely that they're expecting the OS to leave them alone.
      
      Measured to save around 5W on an idle Thinkpad X220.
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      Signed-off-by: default avatarJesse Barnes <jbarnes@virtuousgeek.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      2dcce0a3
  3. 03 Feb, 2012 37 commits