From b607eddd7122595bbcf49c00192faf3e49b142d3 Mon Sep 17 00:00:00 2001 From: Alexey Brodkin Date: Mon, 29 Jun 2015 15:24:37 +0300 Subject: [PATCH] ARCv2: guard SLC DMA ops with spinlock SLC maintenance ops need to be serialized by software as there is no inherent buffering / quequing of aux commands. It can silently ignore a new aux operation if previous one is still ongoing (SLC_CTRL_BUSY) So gaurd the SLC op using a spin lock The spin lock doesn't seem to be contended even in heavy workloads such as iperf. On FPGA @ 75 MHz. [1] Before this change: ============================================================ # iperf -c 10.42.0.1 ------------------------------------------------------------ Client connecting to 10.42.0.1, TCP port 5001 TCP window size: 43.8 KByte (default) ------------------------------------------------------------ [ 3] local 10.42.0.110 port 38935 connected with 10.42.0.1 port 5001 [ ID] Interval Transfer Bandwidth [ 3] 0.0-10.0 sec 48.4 MBytes 40.6 Mbits/sec ============================================================ [2] After this change: ============================================================ # iperf -c 10.42.0.1 ------------------------------------------------------------ Client connecting to 10.42.0.1, TCP port 5001 TCP window size: 43.8 KByte (default) ------------------------------------------------------------ [ 3] local 10.42.0.243 port 60248 connected with 10.42.0.1 port 5001 [ ID] Interval Transfer Bandwidth [ 3] 0.0-10.0 sec 47.5 MBytes 39.8 Mbits/sec # iperf -c 10.42.0.1 ------------------------------------------------------------ Client connecting to 10.42.0.1, TCP port 5001 TCP window size: 43.8 KByte (default) ------------------------------------------------------------ [ 3] local 10.42.0.243 port 60249 connected with 10.42.0.1 port 5001 [ ID] Interval Transfer Bandwidth [ 3] 0.0-10.0 sec 54.9 MBytes 46.0 Mbits/sec ============================================================ Signed-off-by: Alexey Brodkin Cc: arc-linux-dev@synopsys.com Signed-off-by: Vineet Gupta --- arch/arc/mm/cache.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/arc/mm/cache.c b/arch/arc/mm/cache.c index b29d62e..1cd6695 100644 --- a/arch/arc/mm/cache.c +++ b/arch/arc/mm/cache.c @@ -468,10 +468,18 @@ static void __ic_line_inv_vaddr(unsigned long paddr, unsigned long vaddr, noinline void slc_op(unsigned long paddr, unsigned long sz, const int op) { #ifdef CONFIG_ISA_ARCV2 + /* + * SLC is shared between all cores and concurrent aux operations from + * multiple cores need to be serialized using a spinlock + * A concurrent operation can be silently ignored and/or the old/new + * operation can remain incomplete forever (lockup in SLC_CTRL_BUSY loop + * below) + */ + static DEFINE_SPINLOCK(lock); unsigned long flags; unsigned int ctrl; - local_irq_save(flags); + spin_lock_irqsave(&lock, flags); /* * The Region Flush operation is specified by CTRL.RGN_OP[11..9] @@ -504,7 +512,7 @@ noinline void slc_op(unsigned long paddr, unsigned long sz, const int op) while (read_aux_reg(ARC_REG_SLC_CTRL) & SLC_CTRL_BUSY); - local_irq_restore(flags); + spin_unlock_irqrestore(&lock, flags); #endif } -- 2.7.4