From 9ff0bb5ba60638a688a46e93df8c5009896672eb Mon Sep 17 00:00:00 2001 From: Thomas Petazzoni Date: Mon, 20 Oct 2014 19:42:18 +0100 Subject: [PATCH] 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 Signed-off-by: Russell King --- arch/arm/mm/highmem.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c index 45aeaaca9052..e17ed00828d7 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(); -- 2.20.1