The patch titled
Subject: resource: avoid unnecessary lookups in find_next_iomem_res()
has been added to the -mm tree. Its filename is
resource-avoid-unnecessary-lookups-in-find_next_iomem_res.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/resource-avoid-unnecessary-lookups-in-find_next_iomem_res.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/resource-avoid-unnecessary-lookups-in-find_next_iomem_res.patch
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------------------------------------------------------
From: Nadav Amit <namit@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx
Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Toshi Kani <toshi.kani@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/resource.c | 29 ++++++++++++++++++++++-------
1 file changed, 22 insertions(+), 7 deletions(-)
--- a/kernel/resource.c~resource-avoid-unnecessary-lookups-in-find_next_iomem_res
+++ a/kernel/resource.c
@@ -342,6 +342,7 @@ static int find_next_iomem_res(resource_
unsigned long flags, unsigned long desc,
bool first_lvl, struct resource *res)
{
+ bool siblings_only = true;
struct resource *p;
if (!res)
@@ -352,17 +353,31 @@ static int find_next_iomem_res(resource_
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))
- break;
+
+ /* 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;
}
if (p) {
_
Patches currently in -mm which might be from namit@xxxxxxxxxx are
resource-fix-locking-in-find_next_iomem_res.patch
resource-avoid-unnecessary-lookups-in-find_next_iomem_res.patch
resource-introduce-resource-cache.patch
