[PATCH] Support for assymmetric SMP

[PATCH] Support for assymmetric SMP

[Kurt Garloff]

[-- Attachment #1.1: Type: text/plain, Size: 1131 bytes --]

Hi,

some time ago (2.4.2 time), I created a patch that allows using a
multiprocessor system with different speed ix86 CPUs and Linux.

The patch does the following:
* Make sure we got the flags right (in case they are different) before we
  enable XMM/FXSR/.... Right means common subset of supported features.
* Make cpu_khz a per CPU field and use it in the fast_get_timeofday(). The
  offset from last timer tick also must be per CPU.

The patch works fine, but it has a limited scope: It does not try to teach
the scheduler about the fact that the CPUs are different. So a process that
runs on the slower CPU does not get any bonus. It's just unlucky ...
(Some dynamic prio weighting with the cpu_khz should not be too hard in the
 goodness calc, but I wanted to keep things simple.)

I attach the patch against 2.4.16.

Chandra, this is what you've been looking for, right?

Enjoy!
-- 
Kurt Garloff  <garloff@suse.de>                          Eindhoven, NL
GPG key: See mail header, key servers         Linux kernel development
SuSE Linux AG, Nuernberg, DE                            SCSI, Security

[-- Attachment #1.2: 2.4.16-AMP-support.diff --]
[-- Type: text/plain, Size: 13370 bytes --]

--- ./arch/i386/kernel/nmi.c.orig	Fri Jan 18 22:39:20 2002
+++ ./arch/i386/kernel/nmi.c	Sat Mar  9 15:10:30 2002
@@ -161,6 +161,8 @@
 {
 	int i;
 	unsigned int evntsel;
+	int cpu = smp_processor_id();
+	struct cpuinfo_x86 *c = &cpu_data[cpu];
 
 	nmi_perfctr_msr = MSR_K7_PERFCTR0;
 
@@ -175,8 +177,8 @@
 		| K7_NMI_EVENT;
 
 	wrmsr(MSR_K7_EVNTSEL0, evntsel, 0);
-	Dprintk("setting K7_PERFCTR0 to %08lx\n", -(cpu_khz/nmi_hz*1000));
-	wrmsr(MSR_K7_PERFCTR0, -(cpu_khz/nmi_hz*1000), -1);
+	Dprintk("setting K7_PERFCTR0 to %08lx\n", -(c->cpu_khz/nmi_hz*1000));
+	wrmsr(MSR_K7_PERFCTR0, -(c->cpu_khz/nmi_hz*1000), -1);
 	apic_write(APIC_LVTPC, APIC_DM_NMI);
 	evntsel |= K7_EVNTSEL_ENABLE;
 	wrmsr(MSR_K7_EVNTSEL0, evntsel, 0);
@@ -186,6 +188,8 @@
 {
 	int i;
 	unsigned int evntsel;
+	int cpu = smp_processor_id();
+	struct cpuinfo_x86 *c = &cpu_data[cpu];
 
 	nmi_perfctr_msr = MSR_IA32_PERFCTR0;
 
@@ -200,8 +204,8 @@
 		| P6_NMI_EVENT;
 
 	wrmsr(MSR_IA32_EVNTSEL0, evntsel, 0);
-	Dprintk("setting IA32_PERFCTR0 to %08lx\n", -(cpu_khz/nmi_hz*1000));
-	wrmsr(MSR_IA32_PERFCTR0, -(cpu_khz/nmi_hz*1000), 0);
+	Dprintk("setting IA32_PERFCTR0 to %08lx\n", -(c->cpu_khz/nmi_hz*1000));
+	wrmsr(MSR_IA32_PERFCTR0, -(c->cpu_khz/nmi_hz*1000), 0);
 	apic_write(APIC_LVTPC, APIC_DM_NMI);
 	evntsel |= P6_EVNTSEL0_ENABLE;
 	wrmsr(MSR_IA32_EVNTSEL0, evntsel, 0);
@@ -267,6 +271,7 @@
 	 * the stack NMI-atomically, it's safe to use smp_processor_id().
 	 */
 	int sum, cpu = smp_processor_id();
+	struct cpuinfo_x86 *c = &cpu_data[cpu];
 
 	sum = apic_timer_irqs[cpu];
 
@@ -296,5 +301,5 @@
 		alert_counter[cpu] = 0;
 	}
 	if (nmi_perfctr_msr)
-		wrmsr(nmi_perfctr_msr, -(cpu_khz/nmi_hz*1000), -1);
+		wrmsr(nmi_perfctr_msr, -(c->cpu_khz/nmi_hz*1000), -1);
 }
--- ./arch/i386/kernel/i387.c.orig	Fri Feb 23 19:09:08 2001
+++ ./arch/i386/kernel/i387.c	Sat Mar  9 14:26:15 2002
@@ -28,7 +28,7 @@
  * The _current_ task is using the FPU for the first time
  * so initialize it and set the mxcsr to its default
  * value at reset if we support XMM instructions and then
- * remeber the current task has used the FPU.
+ * remember the current task has used the FPU.
  */
 void init_fpu(void)
 {
--- ./arch/i386/kernel/mpparse.c.orig	Fri Nov  9 23:58:18 2001
+++ ./arch/i386/kernel/mpparse.c	Sat Mar  9 14:30:33 2002
@@ -135,6 +135,8 @@
 static int mpc_record; 
 static struct mpc_config_translation *translation_table[MAX_MPC_ENTRY] __initdata;
 
+unsigned long mp_max_features = 0xffffffff;
+
 void __init MP_processor_info (struct mpc_config_processor *m)
 {
  	int ver, quad, logical_apicid;
@@ -215,6 +217,9 @@
 	}
 
 	num_processors++;
+
+	/* Clear features that are not present on all CPUs */
+	mp_max_features &= m->mpc_featureflag;
 
 	if (m->mpc_apicid > MAX_APICS) {
 		printk("Processor #%d INVALID. (Max ID: %d).\n",
--- ./arch/i386/kernel/setup.c.orig	Sat Dec 22 14:08:42 2001
+++ ./arch/i386/kernel/setup.c	Sat Mar  9 15:03:10 2002
@@ -121,6 +121,9 @@
 struct cpuinfo_x86 boot_cpu_data = { 0, 0, 0, 0, -1, 1, 0, 0, -1 };
 
 unsigned long mmu_cr4_features;
+#ifdef CONFIG_SMP
+extern unsigned long mp_max_features;
+#endif
 
 /*
  * Bus types ..
@@ -160,6 +163,7 @@
 
 static int disable_x86_serial_nr __initdata = 1;
 static int disable_x86_fxsr __initdata = 0;
+static int disable_x86_xmm __initdata = 0;
 
 extern int blk_nohighio;
 
@@ -2372,6 +2376,11 @@
 }
 __setup("nofxsr", x86_fxsr_setup);
 
+int __init x86_xmm_setup(char* s)
+{	disable_x86_xmm = 1;
+	return 1;
+}
+__setup("noxmm", x86_xmm_setup);
 
 /* Standard macro to see if a specific flag is changeable */
 static inline int flag_is_changeable_p(u32 flag)
@@ -2479,6 +2488,8 @@
 	return have_cpuid_p();	/* Check to see if CPUID now enabled? */
 }
 
+
+extern void time_init_cpu(struct cpuinfo_x86 *);
 /*
  * This does the hard work of actually picking apart the CPU stuff...
  */
@@ -2626,6 +2637,10 @@
 		clear_bit(X86_FEATURE_XMM, &c->x86_capability);
 	}
 
+	/* XMM/SSE disabled? */
+	if (disable_x86_xmm)
+		clear_bit(X86_FEATURE_XMM, &c->x86_capability);
+	
 	/* Disable the PN if appropriate */
 	squash_the_stupid_serial_number(c);
 
@@ -2659,7 +2674,12 @@
 		/* AND the already accumulated flags with these */
 		for ( i = 0 ; i < NCAPINTS ; i++ )
 			boot_cpu_data.x86_capability[i] &= c->x86_capability[i];
+		time_init_cpu (c);
 	}
+#if 0 //def CONFIG_SMP
+	else
+		c->x86_capability[0] &= mp_max_features;
+#endif
 
 	printk(KERN_DEBUG "CPU:             Common caps: %08x %08x %08x %08x\n",
 	       boot_cpu_data.x86_capability[0],
@@ -2772,7 +2792,7 @@
 
 	if ( test_bit(X86_FEATURE_TSC, &c->x86_capability) ) {
 		seq_printf(m, "cpu MHz\t\t: %lu.%03lu\n",
-			cpu_khz / 1000, (cpu_khz % 1000));
+			c->cpu_khz / 1000, (c->cpu_khz % 1000));
 	}
 
 	/* Cache size */
--- ./arch/i386/kernel/smpboot.c.orig	Fri Jan 18 22:39:20 2002
+++ ./arch/i386/kernel/smpboot.c	Sat Mar  9 14:41:03 2002
@@ -30,6 +30,7 @@
  *		Tigran Aivazian	:	fixed "0.00 in /proc/uptime on SMP" bug.
  *	Maciej W. Rozycki	:	Bits for genuine 82489DX APICs
  *		Martin J. Bligh	: 	Added support for multi-quad systems
+ *		Kurt Garloff	:	Support for SMP with non-identical CPUs
  */
 
 #include <linux/config.h>
@@ -46,6 +47,7 @@
 #include <asm/mtrr.h>
 #include <asm/pgalloc.h>
 #include <asm/smpboot.h>
+#include <asm/bugs.h>
 
 /* Set if we find a B stepping CPU			*/
 static int smp_b_stepping;
@@ -195,7 +197,7 @@
 
 #define NR_LOOPS 5
 
-extern unsigned long fast_gettimeoffset_quotient;
+//extern unsigned long fast_gettimeoffset_quotient;
 
 /*
  * accurate 64-bit/32-bit division, expanded to 32-bit divisions and 64-bit
@@ -236,7 +238,7 @@
 
 	printk("checking TSC synchronization across CPUs: ");
 
-	one_usec = ((1<<30)/fast_gettimeoffset_quotient)*(1<<2);
+	one_usec = ((1<<30)/current_cpu_data.fast_gettimeoffset_quotient)*(1<<2);
 
 	atomic_set(&tsc_start_flag, 1);
 	wmb();
@@ -339,6 +341,38 @@
 }
 #undef NR_LOOPS
 
+/* Note: cpu_boot_data caps on SMP machines is filled in as follows:
+ * (1) Initialized with the boot CPU's caps (head.S)
+ * (2) AND with the common caps from the MP table (identify_cpu())
+ * (3) AND with the caps from the started CPUs (identify_cpu())
+ * (4) Finally calculated and overwritten here (smp_make_common_caps())
+ * Step 2 is actually disabled, as the info is not very reliable.
+ * Step 4 should not be needed then, actually.
+ * KG <garloff@suse.de>, 2001-03-21
+ */
+
+/* Store common subset of capabilities in boot_cpu_data */
+void smp_make_common_caps(void)
+{
+	int cpu, c;
+	unsigned long x86cap[NCAPINTS];
+	for (c = 0; c < NCAPINTS; c++)
+		x86cap[c] = 0xffffffff;
+	for (cpu = 0; cpu < NR_CPUS; cpu++) {
+		if (!(cpu_online_map & (1<<cpu)))
+			continue;
+		for (c = 0; c < NCAPINTS; c++)
+			x86cap[c] &= cpu_data[cpu].x86_capability[c];
+	}
+	for (c = 0; c < NCAPINTS; c++)
+		boot_cpu_data.x86_capability[c] = x86cap[c];
+	printk("CPU: Common caps: %08x %08x %08x %08x\n",
+	       boot_cpu_data.x86_capability[0],
+	       boot_cpu_data.x86_capability[1],
+	       boot_cpu_data.x86_capability[2],
+	       boot_cpu_data.x86_capability[3]);
+}
+
 extern void calibrate_delay(void);
 
 static atomic_t init_deasserted;
@@ -925,6 +959,7 @@
 {
 	unsigned long cachesize;       /* kB   */
 	unsigned long bandwidth = 350; /* MB/s */
+	unsigned long cpu_khz	= boot_cpu_data.cpu_khz;
 	/*
 	 * Rough estimation for SMP scheduling, this is the number of
 	 * cycles it takes for a fully memory-limited process to flush
@@ -981,6 +1016,12 @@
                         (u_long) xquad_portio, (u_long) XQUAD_PORTIO_LEN);
         }
 
+	/* Pieces from check_bugs() ... */
+	identify_cpu(&boot_cpu_data);
+	printk("Boot CPU: ");
+	print_cpu_info(&boot_cpu_data);
+	check_config();
+	
 #ifdef CONFIG_MTRR
 	/*  Must be done before other processors booted  */
 	mtrr_init_boot_cpu ();
@@ -1181,5 +1222,6 @@
 		synchronize_tsc_bp();
 
 smp_done:
+	smp_make_common_caps ();
 	zap_low_mappings();
 }
--- ./arch/i386/kernel/time.c.orig	Sun Nov 11 19:20:21 2001
+++ ./arch/i386/kernel/time.c	Sat Mar  9 14:26:15 2002
@@ -64,19 +64,19 @@
 #include <linux/irq.h>
 
 
-unsigned long cpu_khz;	/* Detected as we calibrate the TSC */
+//unsigned long cpu_khz;	/* Detected as we calibrate the TSC */
 
 /* Number of usecs that the last interrupt was delayed */
 static int delay_at_last_interrupt;
 
-static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
+//static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
 
 /* Cached *multiplier* to convert TSC counts to microseconds.
  * (see the equation below).
  * Equal to 2^32 * (1 / (clocks per usec) ).
  * Initialized in time_init.
  */
-unsigned long fast_gettimeoffset_quotient;
+//unsigned long fast_gettimeoffset_quotient;
 
 extern rwlock_t xtime_lock;
 extern unsigned long wall_jiffies;
@@ -92,7 +92,7 @@
 	rdtsc(eax,edx);
 
 	/* .. relative to previous jiffy (32 bits is enough) */
-	eax -= last_tsc_low;	/* tsc_low delta */
+	eax -= current_cpu_data.last_tsc_low;	/* tsc_low delta */
 
 	/*
          * Time offset = (tsc_low delta) * fast_gettimeoffset_quotient
@@ -105,7 +105,7 @@
 
 	__asm__("mull %2"
 		:"=a" (eax), "=d" (edx)
-		:"rm" (fast_gettimeoffset_quotient),
+		:"rm" (current_cpu_data.fast_gettimeoffset_quotient),
 		 "0" (eax));
 
 	/* our adjusted time offset in microseconds */
@@ -275,8 +275,8 @@
 		if (lost)
 			usec += lost * (1000000 / HZ);
 	}
-	sec = xtime.tv_sec;
-	usec += xtime.tv_usec;
+	sec = current_cpu_data.xtime.tv_sec;
+	usec += current_cpu_data.xtime.tv_usec;
 	read_unlock_irqrestore(&xtime_lock, flags);
 
 	while (usec >= 1000000) {
@@ -440,6 +440,7 @@
 		else
 			last_rtc_update = xtime.tv_sec - 600; /* do it again in 60 s */
 	}
+	current_cpu_data.xtime = xtime;
 	    
 #ifdef CONFIG_MCA
 	if( MCA_bus ) {
@@ -494,7 +495,7 @@
 	
 		/* read Pentium cycle counter */
 
-		rdtscl(last_tsc_low);
+		rdtscl(current_cpu_data.last_tsc_low);
 
 		spin_lock(&i8253_lock);
 		outb_p(0x00, 0x43);     /* latch the count ASAP */
@@ -597,7 +598,7 @@
 		} while ((inb(0x61) & 0x20) == 0);
 		rdtsc(endlow,endhigh);
 
-		last_tsc_low = endlow;
+		current_cpu_data.last_tsc_low = endlow;
 
 		/* Error: ECTCNEVERSET */
 		if (count <= 1)
@@ -634,7 +635,8 @@
 	return 0;
 }
 
-void __init time_init(void)
+
+void __init time_init_cpu(struct cpuinfo_x86 *c)
 {
 	extern int x86_udelay_tsc;
 	
@@ -671,7 +673,8 @@
 	if (cpu_has_tsc) {
 		unsigned long tsc_quotient = calibrate_tsc();
 		if (tsc_quotient) {
-			fast_gettimeoffset_quotient = tsc_quotient;
+			unsigned long cpu_khz;
+			c->fast_gettimeoffset_quotient = tsc_quotient;
 			use_tsc = 1;
 			/*
 			 *	We could be more selective here I suspect
@@ -694,6 +697,7 @@
 	                	"0" (eax), "1" (edx));
 				printk("Detected %lu.%03lu MHz processor.\n", cpu_khz / 1000, cpu_khz % 1000);
 			}
+			c->cpu_khz = cpu_khz;
 		}
 	}
 
@@ -714,4 +718,11 @@
 #else
 	setup_irq(0, &irq0);
 #endif
+}
+
+extern struct cpuinfo_x86 boot_cpu_data;
+
+void inline __init time_init (void)
+{
+	time_init_cpu (&boot_cpu_data);
 }
--- ./init/main.c.orig	Fri Jan 18 22:39:20 2002
+++ ./init/main.c	Sat Mar  9 14:42:03 2002
@@ -608,7 +608,6 @@
 #if defined(CONFIG_SYSVIPC)
 	ipc_init();
 #endif
-	check_bugs();
 
 	/*
 	 *      We count on the initial thread going ok
@@ -616,6 +615,7 @@
 	 *      make syscalls (and thus be locked).
 	 */
 	smp_init();
+	check_bugs();
 
 	/*
 	 * Finally, we wait for all other CPU's, and initialize this
--- ./include/asm-i386/bugs.h.orig	Mon Mar  4 00:43:34 2002
+++ ./include/asm-i386/bugs.h	Sat Mar  9 14:47:09 2002
@@ -21,6 +21,7 @@
  */
 
 #include <linux/config.h>
+#include <linux/utsname.h>
 #include <asm/processor.h>
 #include <asm/i387.h>
 #include <asm/msr.h>
@@ -204,12 +205,16 @@
 
 static void __init check_bugs(void)
 {
-	identify_cpu(&boot_cpu_data);
+	/* identify_cpu(&boot_cpu_data)  and
+	 * check_config()
+	 * are called in smp_boot_cpus() on SMP kernels
+	 */
 #ifndef CONFIG_SMP
+	identify_cpu(&boot_cpu_data);
 	printk("CPU: ");
 	print_cpu_info(&boot_cpu_data);
-#endif
 	check_config();
+#endif
 	check_fpu();
 	check_hlt();
 	check_popad();
--- ./include/asm-i386/processor.h.orig	Mon Mar  4 00:43:33 2002
+++ ./include/asm-i386/processor.h	Sat Mar  9 14:28:55 2002
@@ -17,6 +17,7 @@
 #include <linux/cache.h>
 #include <linux/config.h>
 #include <linux/threads.h>
+#include <linux/time.h>
 
 /*
  * Default implementation of macro that returns current
@@ -53,6 +54,10 @@
 	unsigned long *pmd_quick;
 	unsigned long *pte_quick;
 	unsigned long pgtable_cache_sz;
+	unsigned long cpu_khz;
+	unsigned long fast_gettimeoffset_quotient;
+	unsigned long last_tsc_low;
+	struct timeval xtime;
 } __attribute__((__aligned__(SMP_CACHE_BYTES)));
 
 #define X86_VENDOR_INTEL 0
--- ./include/asm-i386/timex.h.orig	Fri Jan 18 23:05:37 2002
+++ ./include/asm-i386/timex.h	Sat Mar  9 14:42:47 2002
@@ -45,6 +45,6 @@
 #endif
 }
 
-extern unsigned long cpu_khz;
+//extern unsigned long cpu_khz;
 
 #endif

[-- Attachment #2: Type: application/pgp-signature, Size: 232 bytes --]

Re: [PATCH] Support for assymmetric SMP

[Andrea Arcangeli]

On Mon, Mar 11, 2002 at 04:34:21AM +0100, Kurt Garloff wrote:
> @@ -53,6 +54,10 @@
>  	unsigned long *pmd_quick;
>  	unsigned long *pte_quick;
>  	unsigned long pgtable_cache_sz;
> +	unsigned long cpu_khz;
> +	unsigned long fast_gettimeoffset_quotient;
> +	unsigned long last_tsc_low;
> +	struct timeval xtime;
>  } __attribute__((__aligned__(SMP_CACHE_BYTES)));
>  
>  #define X86_VENDOR_INTEL 0

the only problem is if you happen to get the timer irq always in the
same cpu for a few seconds, then the last_tsc_low will wrap around and
gettimeofday will be wrong. And even if you snapshot the full 64bit of the
tsc you'll run into some trouble if the timer irq will be delivered only
to the same cpu for a long time (for example if you use irq bindings).
you'd lose precision and you'll run into the measuration errors of
fast_gettimeoffset_quotient. The right support for asynchronous TSC
handling is a bit more complicated unfortunately.

Andrea

Re: [PATCH] Support for assymmetric SMP

[Kurt Garloff]

[-- Attachment #1: Type: text/plain, Size: 1509 bytes --]

Hi Andrea,

On Mon, Mar 11, 2002 at 05:29:54AM +0100, Andrea Arcangeli wrote:
> the only problem is if you happen to get the timer irq always in the
> same cpu for a few seconds, then the last_tsc_low will wrap around and
> gettimeofday will be wrong. And even if you snapshot the full 64bit of the
> tsc you'll run into some trouble if the timer irq will be delivered only
> to the same cpu for a long time (for example if you use irq bindings).
> you'd lose precision and you'll run into the measuration errors of
> fast_gettimeoffset_quotient. The right support for asynchronous TSC
> handling is a bit more complicated unfortunately.

If your APIC works, your CPUs should get the timer IRQs in alternating order.
At least that is what seems to happen on the SMP box where I created and
tested this patch. It works perfectly there.

In the more general case, you may need to do more, right.
You could make the xtime global again and send IPIs for every timer
interrupt to make all CPUs update their TSC offset.
Storing the full 64bit TSC may be a good option though.

So, if people wanted to have this included I'd rather document the
limitations (don't bind the timer IRQ to one CPU) than introducing
complexity which may hurt the normal SMP user.

Regards,
-- 
Kurt Garloff  <garloff@suse.de>                          Eindhoven, NL
GPG key: See mail header, key servers         Linux kernel development
SuSE Linux AG, Nuernberg, DE                            SCSI, Security

[-- Attachment #2: Type: application/pgp-signature, Size: 232 bytes --]

Re: [PATCH] Support for assymmetric SMP

[Andrea Arcangeli]

On Mon, Mar 11, 2002 at 12:25:49PM +0100, Kurt Garloff wrote:
> Hi Andrea,
> 
> On Mon, Mar 11, 2002 at 05:29:54AM +0100, Andrea Arcangeli wrote:
> > the only problem is if you happen to get the timer irq always in the
> > same cpu for a few seconds, then the last_tsc_low will wrap around and
> > gettimeofday will be wrong. And even if you snapshot the full 64bit of the
> > tsc you'll run into some trouble if the timer irq will be delivered only
> > to the same cpu for a long time (for example if you use irq bindings).
> > you'd lose precision and you'll run into the measuration errors of
> > fast_gettimeoffset_quotient. The right support for asynchronous TSC
> > handling is a bit more complicated unfortunately.
> 
> If your APIC works, your CPUs should get the timer IRQs in alternating order.

Maybe I remeber wrong, but AFIK the io-apic isn't required to scale the
irq load in alternating order, it is perfectly allowed to deliver the
irq always to the same cpu for several seconds. I know the probability
for that to happen is low but it can happen.

Andrea

Re: [PATCH] Support for assymmetric SMP

[Eric W. Biederman]

Andrea Arcangeli <andrea@suse.de> writes:

> On Mon, Mar 11, 2002 at 12:25:49PM +0100, Kurt Garloff wrote:
> > Hi Andrea,
> > 
> > On Mon, Mar 11, 2002 at 05:29:54AM +0100, Andrea Arcangeli wrote:
> > > the only problem is if you happen to get the timer irq always in the
> > > same cpu for a few seconds, then the last_tsc_low will wrap around and
> > > gettimeofday will be wrong. And even if you snapshot the full 64bit of the
> > > tsc you'll run into some trouble if the timer irq will be delivered only
> > > to the same cpu for a long time (for example if you use irq bindings).
> > > you'd lose precision and you'll run into the measuration errors of
> > > fast_gettimeoffset_quotient. The right support for asynchronous TSC
> > > handling is a bit more complicated unfortunately.
> > 
> > If your APIC works, your CPUs should get the timer IRQs in alternating order.
> 
> Maybe I remeber wrong, but AFIK the io-apic isn't required to scale the
> irq load in alternating order, it is perfectly allowed to deliver the
> irq always to the same cpu for several seconds. I know the probability
> for that to happen is low but it can happen.

Actually I know of at least one dual P4 Xeon board where I haven't seen anything
except IPI go to the second cpu.

Eric

Re: [PATCH] Support for assymmetric SMP

[Alan Cox]

> > irq always to the same cpu for several seconds. I know the probability
> > for that to happen is low but it can happen.
> 
> Actually I know of at least one dual P4 Xeon board where I haven't seen anything
> except IPI go to the second cpu.

Expect that to occur. The random distribution stuff doesn't seem to be a
feature of all pentium IV systems. Ie this bug does want fixing

Re: [PATCH] Support for assymmetric SMP

[Martin J. Bligh]

>> Actually I know of at least one dual P4 Xeon board where I 
>> haven't seen anything except IPI go to the second cpu.
> 
> Expect that to occur. The random distribution stuff doesn't seem to be a
> feature of all pentium IV systems. Ie this bug does want fixing

Dave Olien published a patch which will make this issue much
better for P4 - setting the TPR so we route interrupts according 
to how important the processors current work is. Should alleviate
the "dump everything on one CPU" P4ness.

Would still be nice to fix this though.

M.

Re: [PATCH] Support for assymmetric SMP

[Frank van de Pol]

On Mon, Mar 11, 2002 at 04:34:21AM +0100, Kurt Garloff wrote:
> Hi,
> 
> some time ago (2.4.2 time), I created a patch that allows using a
> multiprocessor system with different speed ix86 CPUs and Linux.
> 
> The patch does the following:
> * Make sure we got the flags right (in case they are different) before we
>   enable XMM/FXSR/.... Right means common subset of supported features.

Running quasi symetric system (dual P-II 300 MHz, but different cores, one
is Klamath, other is Deschutes) the fix for the flags is very usefull and
I'd like to see it integrated in the stock kernels. Perhaps the flags and
the (more controversial) speed patches can be split?

Regards,
Frank. 


-- 
+---- --- -- -  -   -    - 
| Frank van de Pol                  -o)    A-L-S-A
| FvdPol@home.nl                    /\\  Sounds good!
| http://www.alsa-project.org      _\_v
| Linux - Why use Windows if we have doors available?