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Thu, 30 Apr 2020 14:12:44 +0000 (UTC) Received: from work-vm (ovpn-114-228.ams2.redhat.com [10.36.114.228]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6018951151; Thu, 30 Apr 2020 14:12:42 +0000 (UTC) Date: Thu, 30 Apr 2020 15:12:39 +0100 From: "Dr. David Alan Gilbert" To: Keqian Zhu Subject: Re: [PATCH v3] migration/throttle: Add cpu-throttle-tailslow migration parameter Message-ID: <20200430141239.GH2874@work-vm> References: <20200413101508.54793-1-zhukeqian1@huawei.com> MIME-Version: 1.0 In-Reply-To: <20200413101508.54793-1-zhukeqian1@huawei.com> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=dgilbert@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/29 23:34:52 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juan Quintela , qemu-devel@nongnu.org, Markus Armbruster , qemu-arm@nongnu.org, wanghaibin.wang@huawei.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Keqian Zhu (zhukeqian1@huawei.com) wrote: > At the tail stage of throttling, the Guest is very sensitive to > CPU percentage while the @cpu-throttle-increment is excessive > usually at tail stage. >=20 > If this parameter is true, we will compute the ideal CPU percentage > used by the Guest, which may exactly make the dirty rate match the > dirty rate threshold. Then we will choose a smaller throttle increment > between the one specified by @cpu-throttle-increment and the one > generated by ideal CPU percentage. >=20 > Therefore, it is compatible to traditional throttling, meanwhile > the throttle increment won't be excessive at tail stage. This may > make migration time longer, and is disabled by default. >=20 > Signed-off-by: Keqian Zhu So I think this is OK; see comment below. Reviewed-by: Dr. David Alan Gilbert > --- > Cc: Juan Quintela > Cc: "Dr. David Alan Gilbert" > Cc: Eric Blake > Cc: Markus Armbruster > --- > migration/migration.c | 13 ++++++++++++ > migration/ram.c | 25 +++++++++++++++++----- > monitor/hmp-cmds.c | 8 ++++++++ > qapi/migration.json | 48 +++++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 89 insertions(+), 5 deletions(-) >=20 > diff --git a/migration/migration.c b/migration/migration.c > index 187ac0410c..d478a87290 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -785,6 +785,8 @@ MigrationParameters *qmp_query_migrate_parameters(Err= or **errp) > params->cpu_throttle_initial =3D s->parameters.cpu_throttle_initial; > params->has_cpu_throttle_increment =3D true; > params->cpu_throttle_increment =3D s->parameters.cpu_throttle_increm= ent; > + params->has_cpu_throttle_tailslow =3D true; > + params->cpu_throttle_tailslow =3D s->parameters.cpu_throttle_tailslo= w; > params->has_tls_creds =3D true; > params->tls_creds =3D g_strdup(s->parameters.tls_creds); > params->has_tls_hostname =3D true; > @@ -1324,6 +1326,10 @@ static void migrate_params_test_apply(MigrateSetPa= rameters *params, > dest->cpu_throttle_increment =3D params->cpu_throttle_increment; > } > =20 > + if (params->has_cpu_throttle_tailslow) { > + dest->cpu_throttle_tailslow =3D params->cpu_throttle_tailslow; > + } > + > if (params->has_tls_creds) { > assert(params->tls_creds->type =3D=3D QTYPE_QSTRING); > dest->tls_creds =3D g_strdup(params->tls_creds->u.s); > @@ -1412,6 +1418,10 @@ static void migrate_params_apply(MigrateSetParamet= ers *params, Error **errp) > s->parameters.cpu_throttle_increment =3D params->cpu_throttle_in= crement; > } > =20 > + if (params->has_cpu_throttle_tailslow) { > + s->parameters.cpu_throttle_tailslow =3D params->cpu_throttle_tai= lslow; > + } > + > if (params->has_tls_creds) { > g_free(s->parameters.tls_creds); > assert(params->tls_creds->type =3D=3D QTYPE_QSTRING); > @@ -3594,6 +3604,8 @@ static Property migration_properties[] =3D { > 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, > @@ -3700,6 +3712,7 @@ static void migration_instance_init(Object *obj) > params->has_throttle_trigger_threshold =3D true; > params->has_cpu_throttle_initial =3D true; > params->has_cpu_throttle_increment =3D true; > + params->has_cpu_throttle_tailslow =3D true; > params->has_max_bandwidth =3D true; > params->has_downtime_limit =3D true; > params->has_x_checkpoint_delay =3D true; > diff --git a/migration/ram.c b/migration/ram.c > index 04f13feb2e..3317c99786 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -616,20 +616,34 @@ static size_t save_page_header(RAMState *rs, QEMUFi= le *f, RAMBlock *block, > * able to complete migration. Some workloads dirty memory way too > * fast and will not effectively converge, even with auto-converge. > */ > -static void mig_throttle_guest_down(void) > +static void mig_throttle_guest_down(uint64_t bytes_dirty_period, > + uint64_t bytes_dirty_threshold) > { > MigrationState *s =3D migrate_get_current(); > uint64_t pct_initial =3D s->parameters.cpu_throttle_initial; > - uint64_t pct_icrement =3D s->parameters.cpu_throttle_increment; > + uint64_t pct_increment =3D s->parameters.cpu_throttle_increment; > + bool pct_tailslow =3D s->parameters.cpu_throttle_tailslow; > int pct_max =3D s->parameters.max_cpu_throttle; > =20 > + uint64_t throttle_now =3D cpu_throttle_get_percentage(); > + uint64_t cpu_now, cpu_ideal, 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_icremen= t, > - pct_max)); > + if (!pct_tailslow) { > + throttle_inc =3D pct_increment; > + } else { > + /* Compute the ideal CPU percentage used by Guest, which may > + * make the dirty rate match the dirty rate threshold. */ > + cpu_now =3D 100 - throttle_now; > + cpu_ideal =3D cpu_now * (bytes_dirty_threshold * 1.0 / > + bytes_dirty_period); I worry if we need a divide-by-0 check; but that seems unlikely. Now if that worked out as huge, then I think the MIN's guard it even with overflow below, so I think we're OK. > + throttle_inc =3D MIN(cpu_now - cpu_ideal, pct_increment); > + } > + cpu_throttle_set(MIN(throttle_now + throttle_inc, pct_max)); > } > } > =20 > @@ -919,7 +933,8 @@ static void migration_trigger_throttle(RAMState *rs) > (++rs->dirty_rate_high_cnt >=3D 2)) { > trace_migration_throttle(); > rs->dirty_rate_high_cnt =3D 0; > - mig_throttle_guest_down(); > + mig_throttle_guest_down(bytes_dirty_period, > + bytes_dirty_threshold); > } > } > } > diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c > index 9b94e67879..acd7539273 100644 > --- a/monitor/hmp-cmds.c > +++ b/monitor/hmp-cmds.c > @@ -419,6 +419,10 @@ void hmp_info_migrate_parameters(Monitor *mon, const= QDict *qdict) > monitor_printf(mon, "%s: %u\n", > MigrationParameter_str(MIGRATION_PARAMETER_CPU_THROTTLE_INCR= EMENT), > params->cpu_throttle_increment); > + assert(params->has_cpu_throttle_tailslow); > + monitor_printf(mon, "%s: %s\n", > + MigrationParameter_str(MIGRATION_PARAMETER_CPU_THROTTLE_TAIL= SLOW), > + 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)= , > @@ -1271,6 +1275,10 @@ void hmp_migrate_set_parameter(Monitor *mon, const= QDict *qdict) > p->has_cpu_throttle_increment =3D true; > visit_type_int(v, param, &p->cpu_throttle_increment, &err); > break; > + case MIGRATION_PARAMETER_CPU_THROTTLE_TAILSLOW: > + p->has_cpu_throttle_tailslow =3D true; > + visit_type_bool(v, param, &p->cpu_throttle_tailslow, &err); > + break; > case MIGRATION_PARAMETER_MAX_CPU_THROTTLE: > p->has_max_cpu_throttle =3D true; > visit_type_int(v, param, &p->max_cpu_throttle, &err); > diff --git a/qapi/migration.json b/qapi/migration.json > index eca2981d0a..ee6c5a0cae 100644 > --- a/qapi/migration.json > +++ b/qapi/migration.json > @@ -552,6 +552,21 @@ > # auto-converge detects that migration is not m= aking > # progress. The default value is 10. (Since 2.7= ) > # > +# @cpu-throttle-tailslow: Make CPU throttling slower at tail stage > +# At the tail stage of throttling, the Guest is = very > +# sensitive to CPU percentage while the @cpu-thr= ottle > +# -increment is excessive usually at tail stage. > +# If this parameter is true, we will compute the= ideal > +# CPU percentage used by the Guest, which may ex= actly make > +# the dirty rate match the dirty rate threshold.= Then we > +# will choose a smaller throttle increment betwe= en the > +# one specified by @cpu-throttle-increment and t= he one > +# generated by ideal CPU percentage. > +# Therefore, it is compatible to traditional thr= ottling, > +# meanwhile the throttle increment won't be exce= ssive > +# at tail stage. > +# The default value is false. (Since 5.1) > +# > # @tls-creds: ID of the 'tls-creds' object that provides credentials for > # establishing a TLS connection over the migration data chan= nel. > # On the outgoing side of the migration, the credentials mus= t > @@ -631,6 +646,7 @@ > 'compress-level', 'compress-threads', 'decompress-threads', > 'compress-wait-thread', 'throttle-trigger-threshold', > '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', > @@ -676,6 +692,21 @@ > # auto-converge detects that migration is not m= aking > # progress. The default value is 10. (Since 2.7= ) > # > +# @cpu-throttle-tailslow: Make CPU throttling slower at tail stage > +# At the tail stage of throttling, the Guest is = very > +# sensitive to CPU percentage while the @cpu-thr= ottle > +# -increment is excessive usually at tail stage. > +# If this parameter is true, we will compute the= ideal > +# CPU percentage used by the Guest, which may ex= actly make > +# the dirty rate match the dirty rate threshold.= Then we > +# will choose a smaller throttle increment betwe= en the > +# one specified by @cpu-throttle-increment and t= he one > +# generated by ideal CPU percentage. > +# Therefore, it is compatible to traditional thr= ottling, > +# meanwhile the throttle increment won't be exce= ssive > +# at tail stage. > +# The default value is false. (Since 5.1) > +# > # @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 creden= tials > @@ -763,6 +794,7 @@ > '*throttle-trigger-threshold': 'int', > '*cpu-throttle-initial': 'int', > '*cpu-throttle-increment': 'int', > + '*cpu-throttle-tailslow': 'bool', > '*tls-creds': 'StrOrNull', > '*tls-hostname': 'StrOrNull', > '*tls-authz': 'StrOrNull', > @@ -834,6 +866,21 @@ > # auto-converge detects that migration is not m= aking > # progress. (Since 2.7) > # > +# @cpu-throttle-tailslow: Make CPU throttling slower at tail stage > +# At the tail stage of throttling, the Guest is = very > +# sensitive to CPU percentage while the @cpu-thr= ottle > +# -increment is excessive usually at tail stage. > +# If this parameter is true, we will compute the= ideal > +# CPU percentage used by the Guest, which may ex= actly make > +# the dirty rate match the dirty rate threshold.= Then we > +# will choose a smaller throttle increment betwe= en the > +# one specified by @cpu-throttle-increment and t= he one > +# generated by ideal CPU percentage. > +# Therefore, it is compatible to traditional thr= ottling, > +# meanwhile the throttle increment won't be exce= ssive > +# at tail stage. > +# The default value is false. (Since 5.1) > +# > # @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 creden= tials > @@ -921,6 +968,7 @@ > '*throttle-trigger-threshold': 'uint8', > '*cpu-throttle-initial': 'uint8', > '*cpu-throttle-increment': 'uint8', > + '*cpu-throttle-tailslow': 'bool', > '*tls-creds': 'str', > '*tls-hostname': 'str', > '*tls-authz': 'str', > --=20 > 2.19.1 >=20 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK