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) { _
