linux-kernel - [PATCH 0/3] resource: find_next_iomem

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Date:   Wed, 12 Jun 2019 21:59:00 -0700
From:   Nadav Amit <namit@...are.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Nadav Amit <namit@...are.com>, Borislav Petkov <bp@...e.de>,
        Toshi Kani <toshi.kani@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 0/3] resource: find_next_iomem_res() improvements

Running some microbenchmarks on dax keeps showing find_next_iomem_res()
as a place in which significant amount of time is spent. It appears that
in order to determine the cacheability that is required for the PTE,
lookup_memtype() is called, and this one traverses the resources list in
an inefficient manner. This patch-set tries to improve this situation.

The first patch fixes what appears to be unsafe locking in
find_next_iomem_res().

The second patch improves performance by searching the top level first,
to find a matching range, before going down to the children. The third
patch improves the performance by caching the top level resource of the
last found resource in find_next_iomem_res().

Both of these optimizations are based on the ranges in the top level not
overlapping each other.

Running sysbench on dax (Haswell, pmem emulation, with write_cache
disabled):

  sysbench fileio --file-total-size=3G --file-test-mode=rndwr \
   --file-io-mode=mmap --threads=4 --file-fsync-mode=fdatasync run

Provides the following results:

		events (avg/stddev)
		-------------------
  5.2-rc3:	1247669.0000/16075.39
  +patches:	1293408.5000/7720.69 (+3.5%)

Cc: Borislav Petkov <bp@...e.de>
Cc: Toshi Kani <toshi.kani@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Ingo Molnar <mingo@...nel.org>

Nadav Amit (3):
  resource: Fix locking in find_next_iomem_res()
  resource: Avoid unnecessary lookups in find_next_iomem_res()
  resource: Introduce resource cache

 kernel/resource.c | 96 ++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 79 insertions(+), 17 deletions(-)

-- 
2.20.1