RE: [PATCH] more robust halt_light

[Alex Williamson <alex.williamson@hp.com>]

   Bjorn pointed out that the existing enable/disable_hlt routines that
I copied from the other archs are rather racey.  Here's a new version
that uses atomic ops to avoid that.  Original patch description below.

  This patch adds some i386-ish enable/disable features to the
pal_halt_light cpu idle implementation as well as tries to avoid bad
interactions with certain revs of PAL on McKinley cpus.  Hopefully this
will provide enough flexibility that we can leave it configured on in
the kernel by default.  My latest measurements on a 1.3GHz rx2600 show
that enabling pal_halt_light in the cpu_idle routine saves 23W/cpu on an
idle system.

Thanks,

	Alex

-- 
Alex Williamson                             HP Linux & Open Source Lab

=== arch/ia64/kernel/process.c 1.51 vs edited ==--- 1.51/arch/ia64/kernel/process.c	Sat Feb 28 03:02:47 2004
+++ edited/arch/ia64/kernel/process.c	Wed Mar  3 14:58:24 2004
@@ -39,6 +39,8 @@
 
 #include "sigframe.h"
 
+static atomic_t hlt_counter = ATOMIC_INIT(0);
+
 void (*ia64_mark_idle)(int);
 
 
@@ -159,6 +161,20 @@
 		ia64_do_signal(oldset, scr, in_syscall);
 }
 
+void disable_hlt(void)
+{
+	atomic_inc(&hlt_counter);
+}
+
+EXPORT_SYMBOL(disable_hlt);
+
+void enable_hlt(void)
+{
+	atomic_dec(&hlt_counter);
+}
+
+EXPORT_SYMBOL(enable_hlt);
+
 /*
  * We use this if we don't have any better idle routine..
  */
@@ -166,7 +182,7 @@
 default_idle (void)
 {
 #ifdef CONFIG_IA64_PAL_IDLE
-	if (!need_resched())
+	if (!atomic_read(&hlt_counter) && local_cpu_data->hlt_works_ok && !need_resched())
 		safe_halt();
 #endif
 }
=== arch/ia64/kernel/setup.c 1.68 vs edited ==--- 1.68/arch/ia64/kernel/setup.c	Mon Jan 19 16:38:10 2004
+++ edited/arch/ia64/kernel/setup.c	Wed Mar  3 15:09:39 2004
@@ -76,6 +76,10 @@
 
 unsigned char aux_device_present = 0xaa;        /* XXX remove this when legacy I/O is gone */
 
+#ifdef CONFIG_IA64_PAL_IDLE
+static unsigned char nohlt;
+#endif
+
 /*
  * The merge_mask variable needs to be set to (max(iommu_page_size(iommu)) - 1).  This
  * mask specifies a mask of address bits that must be 0 in order for two buffers to be
@@ -429,13 +433,20 @@
 		   "revision   : %u\n"
 		   "archrev    : %u\n"
 		   "features   :%s\n"	/* don't change this---it _is_ right! */
+#ifdef CONFIG_IA64_PAL_IDLE
+		   "halt works : %s\n"
+#endif
 		   "cpu number : %lu\n"
 		   "cpu regs   : %u\n"
 		   "cpu MHz    : %lu.%06lu\n"
 		   "itc MHz    : %lu.%06lu\n"
 		   "BogoMIPS   : %lu.%02lu\n\n",
 		   cpunum, c->vendor, family, c->model, c->revision, c->archrev,
-		   features, c->ppn, c->number,
+		   features,
+#ifdef CONFIG_IA64_PAL_IDLE
+		   c->hlt_works_ok ? "yes" : "no",
+#endif
+		   c->ppn, c->number,
 		   c->proc_freq / 1000000, c->proc_freq % 1000000,
 		   c->itc_freq / 1000000, c->itc_freq % 1000000,
 		   lpj*HZ/500000, (lpj*HZ/5000) % 100);
@@ -523,6 +534,31 @@
 	}
 	c->unimpl_va_mask = ~((7L<<61) | ((1L << (impl_va_msb + 1)) - 1));
 	c->unimpl_pa_mask = ~((1L<<63) | ((1L << phys_addr_size) - 1));
+
+#ifdef CONFIG_IA64_PAL_IDLE
+	if (!nohlt) {
+
+		c->hlt_works_ok = 1;
+
+#ifdef CONFIG_PERFMON
+		/*
+		 * McKinley has a PAL that in some revisions that doesn't
+		 * behave well with the PMU.  The belief is PAL >= 7.64 will
+		 * fix the problem.
+		 */
+		if (c->family = 0x1f && c->model = 0) {
+			pal_version_u_t min_ver, cur_ver;
+
+			if (ia64_pal_version(&min_ver, &cur_ver) = 0) {
+
+				if (cur_ver.pal_version_s.pv_pal_b_model <= 0x7 &&
+				    cur_ver.pal_version_s.pv_pal_b_rev < 0x64)
+					c->hlt_works_ok = 0;
+			}
+		}
+#endif
+	}
+#endif
 }
 
 void
@@ -674,3 +710,14 @@
 	ia64_patch_mckinley_e9((unsigned long) __start___mckinley_e9_bundles,
 			       (unsigned long) __end___mckinley_e9_bundles);
 }
+
+#ifdef CONFIG_IA64_PAL_IDLE
+static int __init no_halt(char *s)
+{
+	local_cpu_data->hlt_works_ok = 0;
+	nohlt = 1;
+	return 1;
+}
+
+__setup("no-hlt", no_halt);
+#endif
=== include/asm-ia64/processor.h 1.56 vs edited ==--- 1.56/include/asm-ia64/processor.h	Wed Feb 25 15:46:40 2004
+++ edited/include/asm-ia64/processor.h	Wed Mar  3 09:12:46 2004
@@ -180,6 +180,9 @@
 #ifdef CONFIG_NUMA
 	struct ia64_node_data *node_data;
 #endif
+#ifdef CONFIG_IA64_PAL_IDLE
+	__u8 hlt_works_ok;
+#endif
 };
 
 DECLARE_PER_CPU(struct cpuinfo_ia64, cpu_info);