| Message ID | 1404305055-16769-1-git-send-email-thomas.petazzoni@free-electrons.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 02 Jul 02:44 PM, Thomas Petazzoni wrote: > 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> > --- > 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 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(); What's the status of this one?
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();
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> --- arch/arm/mm/highmem.c | 3 +++ 1 file changed, 3 insertions(+)