From 756398750e11ade1e617cd2a8f8d66fe7ed637e1 Mon Sep 17 00:00:00 2001
From: Nadav Amit <namit@vmware.com>
Date: Thu, 18 Jul 2019 15:57:34 -0700
Subject: [PATCH] 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>
---
kernel/resource.c | 29 ++++++++++++++++++++++-------
1 file changed, 22 insertions(+), 7 deletions(-)
diff --git a/kernel/resource.c b/kernel/resource.c
index 3ced0cd45bdd5..7ea4306503c57 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -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)
@@ -352,17 +353,31 @@ 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))
- 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) {
--
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