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authorThomas Petazzoni <thomas.petazzoni@free-electrons.com>2014-10-20 19:42:18 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2014-10-29 17:22:07 +0000
commit9ff0bb5ba60638a688a46e93df8c5009896672eb (patch)
tree573d0bc5853228e4810a3fe581e920c31293e3bd /arch/arm/mm
parent6d0ec1dd90afa0166a5fdadb1228bb026b09b925 (diff)
ARM: 8180/1: mm: implement no-highmem fast path in kmap_atomic_pfn()
Since CONFIG_HIGHMEM got enabled on ARMv5 Kirkwood, we have noticed a very significant drop in networking performance. The test were conducted on an OpenBlocks A7 board. Without this patch, the outgoing performance measured with iperf are: - highmem OFF, TSO OFF 544 Mbit/s - highmem OFF, TSO ON 942 Mbit/s - highmem ON, TSO OFF 306 Mbit/s - highmem ON, TSO ON 246 Mbit/s On this Kirkwood platform, the L2 cache is a Feroceon cache, and with this cache, all the range operations have to be done on virtual addresses and not physical addresses. Therefore, whenever CONFIG_HIGHMEM is enabled, the cache maintenance operations call kmap_atomic_pfn() and kunmap_atomic(). However, kmap_atomic_pfn() does not implement the same fast path for non-highmem pages as the one implemented in kmap_atomic(), and this is one of the reason for the performance drop. While this patch does not fully restore the performances, it clearly improves them a lot: without patch with patch - highmem ON, TSO OFF 306 Mbit/s 387 Mbit/s - highmem ON, TSO ON 246 Mbit/s 434 Mbit/s We're still far from the !CONFIG_HIGHMEM performances, but it does improve a bit the situation. Thanks a lot to Ezequiel Garcia and Gregory Clement for all the testing work around this topic. Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/mm')
-rw-r--r--arch/arm/mm/highmem.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
index 45aeaaca905..e17ed00828d 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c
@@ -127,8 +127,11 @@ void *kmap_atomic_pfn(unsigned long pfn)
{
unsigned long vaddr;
int idx, type;
+ struct page *page = pfn_to_page(pfn);
pagefault_disable();
+ if (!PageHighMem(page))
+ return page_address(page);
type = kmap_atomic_idx_push();
idx = type + KM_TYPE_NR * smp_processor_id();