RE: [Xen-devel] [PATCH] cpuidle: fix the menu governor to enhance IO performance

["Yu, Ke" <ke.yu@xxxxxxxxx>]

Hi Keir,

Please use the attached version 2 patch. it has the following updates:

- rebase to latest cset 20625, fixing the code conflict (mainly caused by cset 
20611)
- remove hpet irq from I/O multiplier calculation, since hpet is mainly for 
lapic timer broadcast, and not related to I/O request.
- refine the I/O multiplier by using average interrupt interval, which is more 
logically clean and also maintain the performance as v1.

Best Regards
Ke

>-----Original Message-----
>From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Yu, Ke
>Sent: Thursday, December 10, 2009 7:26 PM
>To: Keir Fraser; Wei, Gang
>Cc: Xen-Devel
>Subject: [Xen-devel] [PATCH] cpuidle: fix the menu governor to enhance IO
>performance
>
>cpuidle: fix the menu governor to enhance IO performance
>
>this is a revised version of linux upstream commit
>69d25870f20c4b2563304f2b79c5300dd60a067e:
>"
>    cpuidle: fix the menu governor to boost IO performance
>
>    Fix the menu idle governor which balances power savings, energy efficiency
>    and performance impact.
>
>    The reason for a reworked governor is that there have been serious
>    performance issues reported with the existing code on Nehalem server
>    systems.
>
>    To show this I'm sure Andrew wants to see benchmark results:
>    (benchmark is "fio", "no cstates" is using "idle=poll")
>
>            no cstates  current linux   new algorithm
>    1 disk      107 Mb/s    85 Mb/s     105 Mb/s
>    2 disks     215 Mb/s    123 Mb/s    209 Mb/s
>    12 disks    590 Mb/s    320 Mb/s    585 Mb/s
>
>    In various power benchmark measurements, no degredation was found by
>our
>    measurement&diagnostics team.  Obviously a small percentage more
>power was
>    used in the "fio" benchmark, due to the much higher performance.
>
>    Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
>    Cc: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
>    Cc: Len Brown <lenb@xxxxxxxxxx>
>    Cc: Ingo Molnar <mingo@xxxxxxx>
>    Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
>    Cc: Yanmin Zhang <yanmin_zhang@xxxxxxxxxxxxxxx>
>    Acked-by: Ingo Molnar <mingo@xxxxxxx>
>    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>    Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>"
>
>    in Xen version, most logic is similar and with only one exception: linux 
> use
>nr_iowait
>    and loadavg to track the pending I/O request, which however is not visible 
> to
>Xen. so Xen
>    use the do_irq frequency to estimate the I/O pressure. this is not as 
> accurate
>as linux,
>    and the better approach is to convey guest latency requirement to
>hypervisor by virtual C
>    state. this can be the future enhancement.
>
>    the detail algorithm description is in code comment. with this new 
> algorithm,
>fio
>    benchmark performance improve ~5% with 1 disk. and no power degration is
>found in
>    idle case.
>
>    Signed-off-by: Yu Ke <ke.yu@xxxxxxxxx>
>
>diff -r 8f304c003af4 xen/arch/x86/acpi/cpuidle_menu.c
>--- a/xen/arch/x86/acpi/cpuidle_menu.c
>+++ b/xen/arch/x86/acpi/cpuidle_menu.c
>@@ -30,26 +30,154 @@
> #include <xen/acpi.h>
> #include <xen/timer.h>
> #include <xen/cpuidle.h>
>+#include <asm/irq.h>
>
>-#define BREAK_FUZZ      4       /* 4 us */
>-#define PRED_HISTORY_PCT   50
>-#define USEC_PER_SEC 1000000
>+#define BUCKETS 6
>+#define RESOLUTION 1024
>+#define DECAY 4
>+#define MAX_INTERESTING 50000
>+
>+/*
>+ * Concepts and ideas behind the menu governor
>+ *
>+ * For the menu governor, there are 3 decision factors for picking a C
>+ * state:
>+ * 1) Energy break even point
>+ * 2) Performance impact
>+ * 3) Latency tolerance (TBD: from guest virtual C state)
>+ * These these three factors are treated independently.
>+ *
>+ * Energy break even point
>+ * -----------------------
>+ * C state entry and exit have an energy cost, and a certain amount of time in
>+ * the  C state is required to actually break even on this cost. CPUIDLE
>+ * provides us this duration in the "target_residency" field. So all that we
>+ * need is a good prediction of how long we'll be idle. Like the traditional
>+ * menu governor, we start with the actual known "next timer event" time.
>+ *
>+ * Since there are other source of wakeups (interrupts for example) than
>+ * the next timer event, this estimation is rather optimistic. To get a
>+ * more realistic estimate, a correction factor is applied to the estimate,
>+ * that is based on historic behavior. For example, if in the past the actual
>+ * duration always was 50% of the next timer tick, the correction factor will
>+ * be 0.5.
>+ *
>+ * menu uses a running average for this correction factor, however it uses a
>+ * set of factors, not just a single factor. This stems from the realization
>+ * that the ratio is dependent on the order of magnitude of the expected
>+ * duration; if we expect 500 milliseconds of idle time the likelihood of
>+ * getting an interrupt very early is much higher than if we expect 50 micro
>+ * seconds of idle time.
>+ * For this reason we keep an array of 6 independent factors, that gets
>+ * indexed based on the magnitude of the expected duration
>+ *
>+ * Limiting Performance Impact
>+ * ---------------------------
>+ * C states, especially those with large exit latencies, can have a real
>+ * noticable impact on workloads, which is not acceptable for most sysadmins,
>+ * and in addition, less performance has a power price of its own.
>+ *
>+ * As a general rule of thumb, menu assumes that the following heuristic
>+ * holds:
>+ *     The busier the system, the less impact of C states is acceptable
>+ *
>+ * This rule-of-thumb is implemented using a performance-multiplier:
>+ * If the exit latency times the performance multiplier is longer than
>+ * the predicted duration, the C state is not considered a candidate
>+ * for selection due to a too high performance impact. So the higher
>+ * this multiplier is, the longer we need to be idle to pick a deep C
>+ * state, and thus the less likely a busy CPU will hit such a deep
>+ * C state.
>+ *
>+ * Currently one factors are used in determing this multiplier:
>+ * the do_irq frequency during sampling period (5 milisec), and 4X
>+ * multiplier is added to irq frequency.
>+ * (these values are experimentally determined)
>+ *
>+ */
>+
>+struct perf_factor{
>+    unsigned int last_irq_count;
>+    unsigned int irq_count_sum;
>+    s_time_t    time_stamp;
>+    unsigned int factor;
>+};
>
> struct menu_device
> {
>     int             last_state_idx;
>     unsigned int    expected_us;
>-    unsigned int    predicted_us;
>-    unsigned int    current_predicted_us;
>-    unsigned int    last_measured_us;
>-    unsigned int    elapsed_us;
>+    u64             predicted_us;
>+    unsigned int    measured_us;
>+    unsigned int    exit_us;
>+    unsigned int    bucket;
>+    u64             correction_factor[BUCKETS];
>+    struct perf_factor pf;
> };
>
> static DEFINE_PER_CPU(struct menu_device, menu_devices);
>
>+static inline int which_bucket(unsigned int duration)
>+{
>+   int bucket = 0;
>+
>+   if (duration < 10)
>+       return bucket;
>+   if (duration < 100)
>+       return bucket + 1;
>+   if (duration < 1000)
>+       return bucket + 2;
>+   if (duration < 10000)
>+       return bucket + 3;
>+   if (duration < 100000)
>+       return bucket + 4;
>+   return bucket + 5;
>+}
>+
>+/*
>+ * Return a multiplier for the exit latency that is intended
>+ * to take performance requirements into account.
>+ * The more performance critical we estimate the system
>+ * to be, the higher this multiplier, and thus the higher
>+ * the barrier to go to an expensive C state.
>+ */
>+
>+/* 5 milisec sampling period */
>+#define SAMPLING_PERIOD     5000000
>+
>+/*  4x experimental multiplier for IO intensive */
>+#define IO_MILTIPLIER        4
>+
>+static inline int performance_multiplier(void)
>+{
>+    int mult = 1;
>+    unsigned int factor, irq_count_delta;
>+    struct menu_device *data = &__get_cpu_var(menu_devices);
>+    s_time_t    duration, now;
>+
>+    now = NOW();
>+    duration = now - data->pf.time_stamp;
>+
>+    irq_count_delta = IO_MILTIPLIER *
>+        (this_cpu(irq_count) - data->pf.last_irq_count);
>+
>+    if ( duration < SAMPLING_PERIOD){
>+        mult += (data->pf.factor + irq_count_delta * (DECAY-1)) / DECAY;
>+    }
>+    else{
>+        factor = irq_count_delta * SAMPLING_PERIOD / duration;
>+        data->pf.factor = (data->pf.factor + factor * (DECAY-1)) / DECAY;
>+        data->pf.time_stamp = now;
>+        data->pf.last_irq_count = this_cpu(irq_count);
>+        mult += data->pf.factor;
>+    }
>+
>+    return mult;
>+}
>+
> static unsigned int get_sleep_length_us(void)
> {
>-    s_time_t us = (per_cpu(timer_deadline, smp_processor_id()) - NOW()) /
>1000;
>+    s_time_t us = DIV_ROUND_UP(this_cpu(timer_deadline) - NOW() , 1000);
>     /*
>      * while us < 0 or us > (u32)-1, return a large u32,
>      * choose (unsigned int)-2000 to avoid wrapping while added with exit
>@@ -62,57 +190,86 @@ static int menu_select(struct acpi_proce
> {
>     struct menu_device *data = &__get_cpu_var(menu_devices);
>     int i;
>+    int multiplier;
>
>-    /* determine the expected residency time */
>+    /*  TBD: Change to 0 if C0(polling mode) support is added later*/
>+    data->last_state_idx = CPUIDLE_DRIVER_STATE_START;
>+    data->exit_us = 0;
>+
>+    /* determine the expected residency time, round up */
>     data->expected_us = get_sleep_length_us();
>
>-    /* Recalculate predicted_us based on prediction_history_pct */
>-    data->predicted_us *= PRED_HISTORY_PCT;
>-    data->predicted_us += (100 - PRED_HISTORY_PCT) *
>-        data->current_predicted_us;
>-    data->predicted_us /= 100;
>+    data->bucket = which_bucket(data->expected_us);
>+
>+    multiplier = performance_multiplier();
>+
>+    /*
>+     * if the correction factor is 0 (eg first time init or cpu hotplug
>+     * etc), we actually want to start out with a unity factor.
>+     */
>+    if (data->correction_factor[data->bucket] == 0)
>+        data->correction_factor[data->bucket] = RESOLUTION * DECAY;
>+
>+    /* Make sure to round up for half microseconds */
>+    data->predicted_us = DIV_ROUND(
>+            data->expected_us * data->correction_factor[data->bucket],
>+            RESOLUTION * DECAY);
>
>     /* find the deepest idle state that satisfies our constraints */
>-    for ( i = 2; i < power->count; i++ )
>+    for ( i = CPUIDLE_DRIVER_STATE_START + 1; i < power->count; i++ )
>     {
>         struct acpi_processor_cx *s = &power->states[i];
>
>-        if ( s->target_residency > data->expected_us + s->latency )
>+        if (s->target_residency > data->predicted_us)
>             break;
>-        if ( s->target_residency > data->predicted_us )
>+        if (s->latency * multiplier > data->predicted_us)
>             break;
>         /* TBD: we need to check the QoS requirment in future */
>+        data->exit_us = s->latency;
>+        data->last_state_idx = i;
>     }
>
>-    data->last_state_idx = i - 1;
>-    return i - 1;
>+    return data->last_state_idx;
> }
>
> static void menu_reflect(struct acpi_processor_power *power)
> {
>     struct menu_device *data = &__get_cpu_var(menu_devices);
>-    struct acpi_processor_cx *target = &power->states[data->last_state_idx];
>-    unsigned int last_residency;
>+    unsigned int last_idle_us = power->last_residency;
>     unsigned int measured_us;
>+    u64 new_factor;
>
>-    last_residency = power->last_residency;
>-    measured_us = last_residency + data->elapsed_us;
>+    measured_us = last_idle_us;
>
>-    /* if wrapping, set to max uint (-1) */
>-    measured_us = data->elapsed_us <= measured_us ? measured_us : -1;
>+    /*
>+     * We correct for the exit latency; we are assuming here that the
>+     * exit latency happens after the event that we're interested in.
>+     */
>+    if (measured_us > data->exit_us)
>+        measured_us -= data->exit_us;
>
>-    /* Predict time remaining until next break event */
>-    data->current_predicted_us = max(measured_us, data->last_measured_us);
>+    /* update our correction ratio */
>
>-    /* Distinguish between expected & non-expected events */
>-    if ( last_residency + BREAK_FUZZ
>-         < data->expected_us + target->latency )
>-    {
>-        data->last_measured_us = measured_us;
>-        data->elapsed_us = 0;
>-    }
>+    new_factor = data->correction_factor[data->bucket]
>+        * (DECAY - 1) / DECAY;
>+
>+    if (data->expected_us > 0 && data->measured_us < MAX_INTERESTING)
>+        new_factor += RESOLUTION * measured_us / data->expected_us;
>     else
>-        data->elapsed_us = measured_us;
>+        /*
>+         * we were idle so long that we count it as a perfect
>+         * prediction
>+         */
>+        new_factor += RESOLUTION;
>+
>+    /*
>+     * We don't want 0 as factor; we always want at least
>+     * a tiny bit of estimated time.
>+     */
>+    if (new_factor == 0)
>+        new_factor = 1;
>+
>+    data->correction_factor[data->bucket] = new_factor;
> }
>
> static int menu_enable_device(struct acpi_processor_power *power)
>diff -r 8f304c003af4 xen/arch/x86/irq.c
>--- a/xen/arch/x86/irq.c
>+++ b/xen/arch/x86/irq.c
>@@ -517,6 +517,8 @@ void irq_set_affinity(int irq, cpumask_t
>     cpus_copy(desc->pending_mask, mask);
> }
>
>+DEFINE_PER_CPU(unsigned int, irq_count);
>+
> asmlinkage void do_IRQ(struct cpu_user_regs *regs)
> {
>     struct irqaction *action;
>@@ -527,6 +529,8 @@ asmlinkage void do_IRQ(struct cpu_user_r
>     struct cpu_user_regs *old_regs = set_irq_regs(regs);
>
>     perfc_incr(irqs);
>+
>+    this_cpu(irq_count)++;
>
>     if (irq < 0) {
>         ack_APIC_irq();
>diff -r 8f304c003af4 xen/include/asm-x86/irq.h
>--- a/xen/include/asm-x86/irq.h
>+++ b/xen/include/asm-x86/irq.h
>@@ -105,6 +105,8 @@ extern atomic_t irq_err_count;
> extern atomic_t irq_err_count;
> extern atomic_t irq_mis_count;
>
>+DECLARE_PER_CPU(unsigned int, irq_count);
>+
> int pirq_shared(struct domain *d , int irq);
>
> int map_domain_pirq(struct domain *d, int pirq, int irq, int type,
>diff -r 8f304c003af4 xen/include/xen/cpuidle.h
>--- a/xen/include/xen/cpuidle.h
>+++ b/xen/include/xen/cpuidle.h
>@@ -86,4 +86,6 @@ extern struct cpuidle_governor *cpuidle_
> extern struct cpuidle_governor *cpuidle_current_governor;
> void cpuidle_disable_deep_cstate(void);
>
>+#define CPUIDLE_DRIVER_STATE_START  1
>+
> #endif /* _XEN_CPUIDLE_H */
>diff -r 8f304c003af4 xen/include/xen/lib.h
>--- a/xen/include/xen/lib.h
>+++ b/xen/include/xen/lib.h
>@@ -44,6 +44,7 @@ do {
>    do { typeof(_a) _t = (_a); (_a) = (_b); (_b) = _t; } while ( 0 )
>
> #define DIV_ROUND(x, y) (((x) + (y) / 2) / (y))
>+#define DIV_ROUND_UP(x,y) (((x) + (y) - 1) / (y))
>
> #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]) + __must_be_array(x))

Attachment: cpuidle-io-v2.patch
Description: cpuidle-io-v2.patch

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel