From 756398750e11ade1e617cd2a8f8d66fe7ed637e1 Mon Sep 17 00:00:00 2001 From: Nadav Amit 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 Cc: Borislav Petkov Cc: Toshi Kani Cc: Peter Zijlstra Cc: Dave Hansen Cc: Dan Williams Cc: Bjorn Helgaas Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/resource.c | 29 ++++++++++++++++++++++------- 1 file changed, 22 insertions(+), 7 deletions(-) diff --git a/kernel/resource.c b/kernel/resource.c index 3ced0cd..7ea4306 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) { -- 2.7.4