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author | Thomas Petazzoni <thomas.petazzoni@free-electrons.com> | 2014-10-20 18:42:18 (GMT) |
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committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2014-10-29 17:22:07 (GMT) |
commit | 9ff0bb5ba60638a688a46e93df8c5009896672eb (patch) | |
tree | 573d0bc5853228e4810a3fe581e920c31293e3bd | |
parent | 6d0ec1dd90afa0166a5fdadb1228bb026b09b925 (diff) | |
download | linux-9ff0bb5ba60638a688a46e93df8c5009896672eb.tar.xz |
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>
-rw-r--r-- | arch/arm/mm/highmem.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c index 45aeaac..e17ed00 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(); |