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Re: [PATCH] migration/throttle: Make throttle slower at tail stage
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH] migration/throttle: Make throttle slower at tail stage |
Date: |
Fri, 14 Feb 2020 12:28:10 +0000 |
User-agent: |
Mutt/1.13.3 (2020-01-12) |
* Keqian Zhu (address@hidden) wrote:
> At the tail stage of throttle, VM is very sensitive to
> CPU percentage. We just throttle 30% of remaining CPU
> when throttle is more than 80 percentage.
This is a bit unusual; all of the rest of the throttling has no
fixed constants; all values are set by parameters.
You've got the two, the '80' and the '0.3'
I thinkt he easy solution is to replace your parameter 'tailslow' by two
new parameters; 'tailstart' and 'tailrate'; both defaulting to 100%.
Then you make it:
if (cpu_throttle_now >= pct_tailstart) {
/* Eat some scale of CPU from remaining */
cpu_throttle_inc = ceil((100 - cpu_throttle_now) * pct_tailrate);
(with percentage scaling added).
Then setting 'tailstart' to 80 and 'tailrate' to 30 is equivalent to
what you have, but means we have no magical constants in the code.
Dave
> This doesn't conflict with cpu_throttle_increment.
>
> This may make migration time longer, and is disabled
> by default.
>
> Signed-off-by: Keqian Zhu <address@hidden>
> ---
> Cc: Juan Quintela <address@hidden>
> Cc: "Dr. David Alan Gilbert" <address@hidden>
> Cc: Eric Blake <address@hidden>
> Cc: Markus Armbruster <address@hidden>
> ---
> migration/migration.c | 13 +++++++++++++
> migration/ram.c | 18 ++++++++++++++++--
> monitor/hmp-cmds.c | 4 ++++
> qapi/migration.json | 21 +++++++++++++++++++++
> 4 files changed, 54 insertions(+), 2 deletions(-)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index 3a21a4686c..37b569cee9 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -782,6 +782,8 @@ MigrationParameters *qmp_query_migrate_parameters(Error
> **errp)
> params->cpu_throttle_initial = s->parameters.cpu_throttle_initial;
> params->has_cpu_throttle_increment = true;
> params->cpu_throttle_increment = s->parameters.cpu_throttle_increment;
> + params->has_cpu_throttle_tailslow = true;
> + params->cpu_throttle_tailslow = s->parameters.cpu_throttle_tailslow;
> params->has_tls_creds = true;
> params->tls_creds = g_strdup(s->parameters.tls_creds);
> params->has_tls_hostname = true;
> @@ -1287,6 +1289,10 @@ static void
> migrate_params_test_apply(MigrateSetParameters *params,
> dest->cpu_throttle_increment = params->cpu_throttle_increment;
> }
>
> + if (params->has_cpu_throttle_tailslow) {
> + dest->cpu_throttle_tailslow = params->cpu_throttle_tailslow;
> + }
> +
> if (params->has_tls_creds) {
> assert(params->tls_creds->type == QTYPE_QSTRING);
> dest->tls_creds = g_strdup(params->tls_creds->u.s);
> @@ -1368,6 +1374,10 @@ static void migrate_params_apply(MigrateSetParameters
> *params, Error **errp)
> s->parameters.cpu_throttle_increment =
> params->cpu_throttle_increment;
> }
>
> + if (params->has_cpu_throttle_tailslow) {
> + s->parameters.cpu_throttle_tailslow = params->cpu_throttle_tailslow;
> + }
> +
> if (params->has_tls_creds) {
> g_free(s->parameters.tls_creds);
> assert(params->tls_creds->type == QTYPE_QSTRING);
> @@ -3504,6 +3514,8 @@ static Property migration_properties[] = {
> DEFINE_PROP_UINT8("x-cpu-throttle-increment", MigrationState,
> parameters.cpu_throttle_increment,
> DEFAULT_MIGRATE_CPU_THROTTLE_INCREMENT),
> + DEFINE_PROP_BOOL("x-cpu-throttle-tailslow", MigrationState,
> + parameters.cpu_throttle_tailslow, false),
> DEFINE_PROP_SIZE("x-max-bandwidth", MigrationState,
> parameters.max_bandwidth, MAX_THROTTLE),
> DEFINE_PROP_UINT64("x-downtime-limit", MigrationState,
> @@ -3600,6 +3612,7 @@ static void migration_instance_init(Object *obj)
> params->has_decompress_threads = true;
> params->has_cpu_throttle_initial = true;
> params->has_cpu_throttle_increment = true;
> + params->has_cpu_throttle_tailslow = true;
> params->has_max_bandwidth = true;
> params->has_downtime_limit = true;
> params->has_x_checkpoint_delay = true;
> diff --git a/migration/ram.c b/migration/ram.c
> index ed23ed1c7c..d86413a5d1 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -29,6 +29,7 @@
> #include "qemu/osdep.h"
> #include "cpu.h"
> #include <zlib.h>
> +#include <math.h>
> #include "qemu/cutils.h"
> #include "qemu/bitops.h"
> #include "qemu/bitmap.h"
> @@ -620,15 +621,28 @@ static void mig_throttle_guest_down(void)
> {
> MigrationState *s = migrate_get_current();
> uint64_t pct_initial = s->parameters.cpu_throttle_initial;
> - uint64_t pct_icrement = s->parameters.cpu_throttle_increment;
> + uint64_t pct_increment = s->parameters.cpu_throttle_increment;
> + bool pct_tailslow = s->parameters.cpu_throttle_tailslow;
> int pct_max = s->parameters.max_cpu_throttle;
>
> + const uint64_t cpu_throttle_now = cpu_throttle_get_percentage();
> + uint64_t cpu_throttle_inc;
> +
> /* We have not started throttling yet. Let's start it. */
> if (!cpu_throttle_active()) {
> cpu_throttle_set(pct_initial);
> } else {
> /* Throttling already on, just increase the rate */
> - cpu_throttle_set(MIN(cpu_throttle_get_percentage() + pct_icrement,
> + if (cpu_throttle_now >= 80 && pct_tailslow) {
> + /* Eat some scale of CPU from remaining */
> + cpu_throttle_inc = ceil((100 - cpu_throttle_now) * 0.3);
> + if (cpu_throttle_inc > pct_increment) {
> + cpu_throttle_inc = pct_increment;
> + }
> + } else {
> + cpu_throttle_inc = pct_increment;
> + }
> + cpu_throttle_set(MIN(cpu_throttle_now + cpu_throttle_inc,
> pct_max));
> }
> }
> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> index 558fe06b8f..b5f5c0b382 100644
> --- a/monitor/hmp-cmds.c
> +++ b/monitor/hmp-cmds.c
> @@ -416,6 +416,10 @@ void hmp_info_migrate_parameters(Monitor *mon, const
> QDict *qdict)
> monitor_printf(mon, "%s: %u\n",
>
> MigrationParameter_str(MIGRATION_PARAMETER_CPU_THROTTLE_INCREMENT),
> params->cpu_throttle_increment);
> + assert(params->has_cpu_throttle_tailslow);
> + monitor_printf(mon, "%s: %s\n",
> +
> MigrationParameter_str(MIGRATION_PARAMETER_CPU_THROTTLE_TAILSLOW),
> + params->cpu_throttle_tailslow ? "on" : "off");
> assert(params->has_max_cpu_throttle);
> monitor_printf(mon, "%s: %u\n",
> MigrationParameter_str(MIGRATION_PARAMETER_MAX_CPU_THROTTLE),
> diff --git a/qapi/migration.json b/qapi/migration.json
> index b7348d0c8b..0ac94e00f2 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -532,6 +532,12 @@
> # auto-converge detects that migration is not making
> # progress. The default value is 10. (Since 2.7)
> #
> +# @cpu-throttle-tailslow: Make throttle slower at tail stage
> +# At the tail stage of throttle, VM is very
> sensitive to
> +# CPU percentage. We just throttle 30% of remaining
> CPU
> +# when throttle is more than 80 percentage. The
> default
> +# value is false. (Since 4.1)
> +#
> # @tls-creds: ID of the 'tls-creds' object that provides credentials for
> # establishing a TLS connection over the migration data channel.
> # On the outgoing side of the migration, the credentials must
> @@ -594,6 +600,7 @@
> 'compress-level', 'compress-threads', 'decompress-threads',
> 'compress-wait-thread',
> 'cpu-throttle-initial', 'cpu-throttle-increment',
> + 'cpu-throttle-tailslow',
> 'tls-creds', 'tls-hostname', 'tls-authz', 'max-bandwidth',
> 'downtime-limit', 'x-checkpoint-delay', 'block-incremental',
> 'multifd-channels',
> @@ -634,6 +641,12 @@
> # auto-converge detects that migration is not making
> # progress. The default value is 10. (Since 2.7)
> #
> +# @cpu-throttle-tailslow: Make throttle slower at tail stage
> +# At the tail stage of throttle, VM is very
> sensitive to
> +# CPU percentage. We just throttle 30% of remaining
> CPU
> +# when throttle is more than 80 percentage. The
> default
> +# value is false. (Since 4.1)
> +#
> # @tls-creds: ID of the 'tls-creds' object that provides credentials
> # for establishing a TLS connection over the migration data
> # channel. On the outgoing side of the migration, the credentials
> @@ -703,6 +716,7 @@
> '*decompress-threads': 'int',
> '*cpu-throttle-initial': 'int',
> '*cpu-throttle-increment': 'int',
> + '*cpu-throttle-tailslow': 'bool',
> '*tls-creds': 'StrOrNull',
> '*tls-hostname': 'StrOrNull',
> '*tls-authz': 'StrOrNull',
> @@ -767,6 +781,12 @@
> # auto-converge detects that migration is not making
> # progress. (Since 2.7)
> #
> +# @cpu-throttle-tailslow: Make throttle slower at tail stage
> +# At the tail stage of throttle, VM is very
> sensitive to
> +# CPU percentage. We just throttle 30% of remaining
> CPU
> +# when throttle is more than 80 percentage. The
> default
> +# value is false. (Since 4.1)
> +#
> # @tls-creds: ID of the 'tls-creds' object that provides credentials
> # for establishing a TLS connection over the migration data
> # channel. On the outgoing side of the migration, the credentials
> @@ -836,6 +856,7 @@
> '*decompress-threads': 'uint8',
> '*cpu-throttle-initial': 'uint8',
> '*cpu-throttle-increment': 'uint8',
> + '*cpu-throttle-tailslow': 'bool',
> '*tls-creds': 'str',
> '*tls-hostname': 'str',
> '*tls-authz': 'str',
> --
> 2.19.1
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK