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ARCv2: guard SLC DMA ops with spinlock

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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 <abrodkin@synopsys.com>
Cc: arc-linux-dev@synopsys.com
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
This commit is contained in:
Alexey Brodkin 2015-06-29 15:24:37 +03:00 committed by Vineet Gupta
parent 14a0abfc4a
commit b607eddd71
1 changed files with 10 additions and 2 deletions
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12
arch/arc/mm/cache.c
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@ -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
}