Commit 75639875 authored Jul 18, 2019 by Nadav Amit Committed by Linus Torvalds Jul 18, 2019

resource: avoid unnecessary lookups in find_next_iomem_res()

find_next_iomem_res() shows up to be a source for overhead in dax
benchmarks.

Improve performance by not considering children of the tree if the top
level does not match.  Since the range of the parents should include the
range of the children such check is redundant.

Running sysbench on dax (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
  w/patch:	1286320.5000/16402.72	(+3%)

Link: http://lkml.kernel.org/r/20190613045903.4922-3-namit@vmware.com


Signed-off-by: Nadav Amit <namit@vmware.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 49f17c26

kernel/resource.c

+22 −7

Original line number	Diff line number	Diff line
		@@ -342,6 +342,7 @@ static int find_next_iomem_res(resource_size_t start, resource_size_t end,
		unsigned long flags, unsigned long desc,
		bool first_lvl, struct resource *res)
		{
		bool siblings_only = true;
		struct resource *p;

		if (!res)
		@@ -352,16 +353,30 @@ static int find_next_iomem_res(resource_size_t start, resource_size_t end,

		read_lock(&resource_lock);

		for (p = iomem_resource.child; p; p = next_resource(p, first_lvl)) {
		if ((p->flags & flags) != flags)
		continue;
		if ((desc != IORES_DESC_NONE) && (desc != p->desc))
		continue;
		for (p = iomem_resource.child; p; p = next_resource(p, siblings_only)) {
		/* If we passed the resource we are looking for, stop */
		if (p->start > end) {
		p = NULL;
		break;
		}
		if ((p->end >= start) && (p->start <= end))

		/* Skip until we find a range that matches what we look for */
		if (p->end < start)
		continue;

		/*
		* Now that we found a range that matches what we look for,
		* check the flags and the descriptor. If we were not asked to
		* use only the first level, start looking at children as well.
		*/
		siblings_only = first_lvl;

		if ((p->flags & flags) != flags)
		continue;
		if ((desc != IORES_DESC_NONE) && (desc != p->desc))
		continue;

		/* Found a match, break */
		break;
		}

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