From c4d27c4d024f5440497106bb2ae15e9e60f7099c Mon Sep 17 00:00:00 2001 From: Brice Goglin Date: Mon, 19 Aug 2013 11:43:35 +0200 Subject: dmaengine: make dma_channel_rebalance() NUMA aware dma_channel_rebalance() currently distributes channels by processor ID. These IDs often change with the BIOS, and the order isn't related to the DMA channel list (related to PCI bus ids). * On my SuperMicro dual E5 machine, first socket has processor IDs [0-7] (and [16-23] for hyperthreads), second socket has [8-15]+[24-31] => channels are properly allocated to local CPUs. * On Dells R720 with same processors, first socket has even processor IDs, second socket has odd numbers => half the processors get channels on the remote socket, causing cross-NUMA traffic and lower DMA performance. Change nth_chan() to return the channel with min table_count and in the NUMA node of the given CPU, if any. If none, the (non-local) channel with min table_count is returned. nth_chan() is therefore renamed into min_chan() since we don't iterate until the nth channel anymore. In practice, the behavior is the same because first channels are taken first and are then ignored because they got an additional reference. The new code has a slightly higher complexity since we always scan the entire list of channels for finding the minimal table_count (instead of stopping after N chans), and because we check whether the CPU is in the DMA device locality mask. Overall we still have time complexity = number of chans x number of processors. This rebalance is rarely used, so this won't hurt. On the above SuperMicro machine, channels are still allocated the same. On the Dells, there are no locality issue anymore (MEMCPY channel X goes to processor X and to its hyperthread sibling). Signed-off-by: Brice Goglin Signed-off-by: Dan Williams --- drivers/dma/dmaengine.c | 55 ++++++++++++++++++++++++------------------------- 1 file changed, 27 insertions(+), 28 deletions(-) (limited to 'drivers/dma') diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 9e56745..e428cf2 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -376,20 +376,30 @@ void dma_issue_pending_all(void) EXPORT_SYMBOL(dma_issue_pending_all); /** - * nth_chan - returns the nth channel of the given capability + * dma_chan_is_local - returns true if the channel is in the same numa-node as the cpu + */ +static bool dma_chan_is_local(struct dma_chan *chan, int cpu) +{ + int node = dev_to_node(chan->device->dev); + return node == -1 || cpumask_test_cpu(cpu, cpumask_of_node(node)); +} + +/** + * min_chan - returns the channel with min count and in the same numa-node as the cpu * @cap: capability to match - * @n: nth channel desired + * @cpu: cpu index which the channel should be close to * - * Defaults to returning the channel with the desired capability and the - * lowest reference count when 'n' cannot be satisfied. Must be called - * under dma_list_mutex. + * If some channels are close to the given cpu, the one with the lowest + * reference count is returned. Otherwise, cpu is ignored and only the + * reference count is taken into account. + * Must be called under dma_list_mutex. */ -static struct dma_chan *nth_chan(enum dma_transaction_type cap, int n) +static struct dma_chan *min_chan(enum dma_transaction_type cap, int cpu) { struct dma_device *device; struct dma_chan *chan; - struct dma_chan *ret = NULL; struct dma_chan *min = NULL; + struct dma_chan *localmin = NULL; list_for_each_entry(device, &dma_device_list, global_node) { if (!dma_has_cap(cap, device->cap_mask) || @@ -398,27 +408,22 @@ static struct dma_chan *nth_chan(enum dma_transaction_type cap, int n) list_for_each_entry(chan, &device->channels, device_node) { if (!chan->client_count) continue; - if (!min) - min = chan; - else if (chan->table_count < min->table_count) + if (!min || chan->table_count < min->table_count) min = chan; - if (n-- == 0) { - ret = chan; - break; /* done */ - } + if (dma_chan_is_local(chan, cpu)) + if (!localmin || + chan->table_count < localmin->table_count) + localmin = chan; } - if (ret) - break; /* done */ } - if (!ret) - ret = min; + chan = localmin ? localmin : min; - if (ret) - ret->table_count++; + if (chan) + chan->table_count++; - return ret; + return chan; } /** @@ -435,7 +440,6 @@ static void dma_channel_rebalance(void) struct dma_device *device; int cpu; int cap; - int n; /* undo the last distribution */ for_each_dma_cap_mask(cap, dma_cap_mask_all) @@ -454,14 +458,9 @@ static void dma_channel_rebalance(void) return; /* redistribute available channels */ - n = 0; for_each_dma_cap_mask(cap, dma_cap_mask_all) for_each_online_cpu(cpu) { - if (num_possible_cpus() > 1) - chan = nth_chan(cap, n++); - else - chan = nth_chan(cap, -1); - + chan = min_chan(cap, cpu); per_cpu_ptr(channel_table[cap], cpu)->chan = chan; } } -- cgit v1.1