[v2] parisc: Reorder TLB flush timing calculation

Commit Message

John David Anglin Oct. 17, 2018, 12:49 a.m. UTC

On boot (mostly reboot), my c8000 sometimes crashes after it prints the
TLB flush threshold.  The lockup is hard.  The front LED flashes red and
the box must be unplugged to reset the error.

I noticed that when the crash occurs the TLB flush threshold is about
one quarter what it is on a successful boot.  If I disabled the calculation,
the crash didn't occur.  There also seemed to be a timing dependency
affecting the crash.  I finally realized that the flush_tlb_all() timing
test runs just after the secondary CPUs are started.  There seems to be
a problem with running flush_tlb_all() too soon after the CPUs are started.

The timing for the range test always seemed okay.  So, I reversed the order
of the two timing tests and I haven't had a crash at this point so far.

I added a couple of information messages which I have left to help with
diagnosis if the problem should appear on another machine.

This version reduces the minimum TLB flush threshold to 16 KiB.


Signed-off-by: John David Anglin <[e-mail]>

Patch

diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c
index e3b45546d589..22a555e6346b 100644
--- a/arch/parisc/kernel/cache.c
+++ b/arch/parisc/kernel/cache.c
@@ -363,7 +375,7 @@  EXPORT_SYMBOL(flush_kernel_icache_range_asm);
 #define FLUSH_THRESHOLD 0x80000 /* 0.5MB */
 static unsigned long parisc_cache_flush_threshold __read_mostly = FLUSH_THRESHOLD;
 
-#define FLUSH_TLB_THRESHOLD (2*1024*1024) /* 2MB initial TLB threshold */
+#define FLUSH_TLB_THRESHOLD (16*1024) /* 16 KiB minimum TLB threshold */
 static unsigned long parisc_tlb_flush_threshold __read_mostly = FLUSH_TLB_THRESHOLD;
 
 void __init parisc_setup_cache_timing(void)
@@ -403,10 +415,6 @@  void __init parisc_setup_cache_timing(void)
 		goto set_tlb_threshold;
 	}
 
-	alltime = mfctl(16);
-	flush_tlb_all();
-	alltime = mfctl(16) - alltime;
-
 	size = 0;
 	start = (unsigned long) _text;
 	rangetime = mfctl(16);
@@ -417,13 +425,19 @@  void __init parisc_setup_cache_timing(void)
 	}
 	rangetime = mfctl(16) - rangetime;
 
-	printk(KERN_DEBUG "Whole TLB flush %lu cycles, flushing %lu bytes %lu cycles\n",
+	alltime = mfctl(16);
+	flush_tlb_all();
+	alltime = mfctl(16) - alltime;
+
+	printk(KERN_INFO "Whole TLB flush %lu cycles, Range flush %lu bytes %lu cycles\n",
 		alltime, size, rangetime);
 
-	threshold = PAGE_ALIGN(num_online_cpus() * size * alltime / rangetime);
+	threshold = PAGE_ALIGN((num_online_cpus() * size * alltime) / rangetime);
+	printk(KERN_INFO "Calculated TLB flush threshold %lu KiB\n",
+		threshold/1024);
 
 set_tlb_threshold:
-	if (threshold)
+	if (threshold > parisc_tlb_flush_threshold)
 		parisc_tlb_flush_threshold = threshold;
 	printk(KERN_INFO "TLB flush threshold set to %lu KiB\n",
 		parisc_tlb_flush_threshold/1024);