From: Xiubo Li <xiubli@redhat.com>
To: Venky Shankar <vshankar@redhat.com>, Jeff Layton <jlayton@redhat.com>
Cc: Patrick Donnelly <pdonnell@redhat.com>,
ceph-devel <ceph-devel@vger.kernel.org>
Subject: Re: [PATCH v3 2/4] ceph: track average/stdev r/w/m latency
Date: Wed, 22 Sep 2021 21:45:59 +0800 [thread overview]
Message-ID: <f6be2044-c62c-7b57-b3c5-fb5581e7b1ab@redhat.com> (raw)
In-Reply-To: <CACPzV1mA45ByOwdcBQXH0ugq50wzTMuK=WXiP--UG5_mam2ztw@mail.gmail.com>
On 9/22/21 8:33 PM, Venky Shankar wrote:
> On Wed, Sep 22, 2021 at 5:47 PM Jeff Layton <jlayton@redhat.com> wrote:
>> On Tue, 2021-09-21 at 18:37 +0530, Venky Shankar wrote:
>>> Update the math involved to closely mimic how its done in
>>> user land. This does not make a lot of difference to the
>>> execution speed.
>>>
>>> Signed-off-by: Venky Shankar <vshankar@redhat.com>
>>> ---
>>> fs/ceph/metric.c | 63 +++++++++++++++++++++---------------------------
>>> fs/ceph/metric.h | 3 +++
>>> 2 files changed, 31 insertions(+), 35 deletions(-)
>>>
>>> diff --git a/fs/ceph/metric.c b/fs/ceph/metric.c
>>> index 226dc38e2909..ca758bff69ca 100644
>>> --- a/fs/ceph/metric.c
>>> +++ b/fs/ceph/metric.c
>>> @@ -245,6 +245,7 @@ int ceph_metric_init(struct ceph_client_metric *m)
>>>
>>> spin_lock_init(&m->read_metric_lock);
>>> m->read_latency_sq_sum = 0;
>>> + m->avg_read_latency = 0;
>>> m->read_latency_min = KTIME_MAX;
>>> m->read_latency_max = 0;
>>> m->total_reads = 0;
>>> @@ -255,6 +256,7 @@ int ceph_metric_init(struct ceph_client_metric *m)
>>>
>>> spin_lock_init(&m->write_metric_lock);
>>> m->write_latency_sq_sum = 0;
>>> + m->avg_write_latency = 0;
>>> m->write_latency_min = KTIME_MAX;
>>> m->write_latency_max = 0;
>>> m->total_writes = 0;
>>> @@ -265,6 +267,7 @@ int ceph_metric_init(struct ceph_client_metric *m)
>>>
>>> spin_lock_init(&m->metadata_metric_lock);
>>> m->metadata_latency_sq_sum = 0;
>>> + m->avg_metadata_latency = 0;
>>> m->metadata_latency_min = KTIME_MAX;
>>> m->metadata_latency_max = 0;
>>> m->total_metadatas = 0;
>>> @@ -322,20 +325,25 @@ void ceph_metric_destroy(struct ceph_client_metric *m)
>>> max = new; \
>>> }
>>>
>>> -static inline void __update_stdev(ktime_t total, ktime_t lsum,
>>> - ktime_t *sq_sump, ktime_t lat)
>>> +static inline void __update_latency(ktime_t *ctotal, ktime_t *lsum,
>>> + ktime_t *lavg, ktime_t *min, ktime_t *max,
>>> + ktime_t *sum_sq, ktime_t lat)
>>> {
>>> - ktime_t avg, sq;
>>> + ktime_t total, avg;
>>>
>>> - if (unlikely(total == 1))
>>> - return;
>>> + total = ++(*ctotal);
>>> + *lsum += lat;
>>> +
>>> + METRIC_UPDATE_MIN_MAX(*min, *max, lat);
>>>
>>> - /* the sq is (lat - old_avg) * (lat - new_avg) */
>>> - avg = DIV64_U64_ROUND_CLOSEST((lsum - lat), (total - 1));
>>> - sq = lat - avg;
>>> - avg = DIV64_U64_ROUND_CLOSEST(lsum, total);
>>> - sq = sq * (lat - avg);
>>> - *sq_sump += sq;
>>> + if (unlikely(total == 1)) {
>>> + *lavg = lat;
>>> + *sum_sq = 0;
>>> + } else {
>>> + avg = *lavg + div64_s64(lat - *lavg, total);
>>> + *sum_sq += (lat - *lavg)*(lat - avg);
>>> + *lavg = avg;
>>> + }
>>> }
>>>
>>> void ceph_update_read_metrics(struct ceph_client_metric *m,
>>> @@ -343,23 +351,18 @@ void ceph_update_read_metrics(struct ceph_client_metric *m,
>>> unsigned int size, int rc)
>>> {
>>> ktime_t lat = ktime_sub(r_end, r_start);
>>> - ktime_t total;
>>>
>>> if (unlikely(rc < 0 && rc != -ENOENT && rc != -ETIMEDOUT))
>>> return;
>>>
>>> spin_lock(&m->read_metric_lock);
>>> - total = ++m->total_reads;
>>> m->read_size_sum += size;
>>> - m->read_latency_sum += lat;
>>> METRIC_UPDATE_MIN_MAX(m->read_size_min,
>>> m->read_size_max,
>>> size);
>>> - METRIC_UPDATE_MIN_MAX(m->read_latency_min,
>>> - m->read_latency_max,
>>> - lat);
>>> - __update_stdev(total, m->read_latency_sum,
>>> - &m->read_latency_sq_sum, lat);
>>> + __update_latency(&m->total_reads, &m->read_latency_sum,
>>> + &m->avg_read_latency, &m->read_latency_min,
>>> + &m->read_latency_max, &m->read_latency_sq_sum, lat);
>> Do we really need to calculate the std deviation on every update? We
>> have to figure that in most cases, this stuff will be collected but only
>> seldom viewed.
>>
>> ISTM that we ought to collect just the bare minimum of info on each
>> update, and save the more expensive calculations for the tool presenting
>> this info.
> Yeh, that's probably the plan we want going forward when introducing
> new metrics.
>
> FWIW, we could start doing it with this itself. It's just that the
> user land PRs are approved and those do the way it is done here.
>
> I'm ok with moving math crunching to the tool and it should not be a
> major change to this patchset.
Yeah, I am also prefer to do this in the tool instead of here on each
update.
>
>>> spin_unlock(&m->read_metric_lock);
>>> }
>>>
>>> @@ -368,23 +371,18 @@ void ceph_update_write_metrics(struct ceph_client_metric *m,
>>> unsigned int size, int rc)
>>> {
>>> ktime_t lat = ktime_sub(r_end, r_start);
>>> - ktime_t total;
>>>
>>> if (unlikely(rc && rc != -ETIMEDOUT))
>>> return;
>>>
>>> spin_lock(&m->write_metric_lock);
>>> - total = ++m->total_writes;
>>> m->write_size_sum += size;
>>> - m->write_latency_sum += lat;
>>> METRIC_UPDATE_MIN_MAX(m->write_size_min,
>>> m->write_size_max,
>>> size);
>>> - METRIC_UPDATE_MIN_MAX(m->write_latency_min,
>>> - m->write_latency_max,
>>> - lat);
>>> - __update_stdev(total, m->write_latency_sum,
>>> - &m->write_latency_sq_sum, lat);
>>> + __update_latency(&m->total_writes, &m->write_latency_sum,
>>> + &m->avg_write_latency, &m->write_latency_min,
>>> + &m->write_latency_max, &m->write_latency_sq_sum, lat);
>>> spin_unlock(&m->write_metric_lock);
>>> }
>>>
>>> @@ -393,18 +391,13 @@ void ceph_update_metadata_metrics(struct ceph_client_metric *m,
>>> int rc)
>>> {
>>> ktime_t lat = ktime_sub(r_end, r_start);
>>> - ktime_t total;
>>>
>>> if (unlikely(rc && rc != -ENOENT))
>>> return;
>>>
>>> spin_lock(&m->metadata_metric_lock);
>>> - total = ++m->total_metadatas;
>>> - m->metadata_latency_sum += lat;
>>> - METRIC_UPDATE_MIN_MAX(m->metadata_latency_min,
>>> - m->metadata_latency_max,
>>> - lat);
>>> - __update_stdev(total, m->metadata_latency_sum,
>>> - &m->metadata_latency_sq_sum, lat);
>>> + __update_latency(&m->total_metadatas, &m->metadata_latency_sum,
>>> + &m->avg_metadata_latency, &m->metadata_latency_min,
>>> + &m->metadata_latency_max, &m->metadata_latency_sq_sum, lat);
>>> spin_unlock(&m->metadata_metric_lock);
>>> }
>>> diff --git a/fs/ceph/metric.h b/fs/ceph/metric.h
>>> index 103ed736f9d2..0af02e212033 100644
>>> --- a/fs/ceph/metric.h
>>> +++ b/fs/ceph/metric.h
>>> @@ -138,6 +138,7 @@ struct ceph_client_metric {
>>> u64 read_size_min;
>>> u64 read_size_max;
>>> ktime_t read_latency_sum;
>>> + ktime_t avg_read_latency;
>>> ktime_t read_latency_sq_sum;
>>> ktime_t read_latency_min;
>>> ktime_t read_latency_max;
>>> @@ -148,6 +149,7 @@ struct ceph_client_metric {
>>> u64 write_size_min;
>>> u64 write_size_max;
>>> ktime_t write_latency_sum;
>>> + ktime_t avg_write_latency;
>>> ktime_t write_latency_sq_sum;
>>> ktime_t write_latency_min;
>>> ktime_t write_latency_max;
>>> @@ -155,6 +157,7 @@ struct ceph_client_metric {
>>> spinlock_t metadata_metric_lock;
>>> u64 total_metadatas;
>>> ktime_t metadata_latency_sum;
>>> + ktime_t avg_metadata_latency;
>>> ktime_t metadata_latency_sq_sum;
>>> ktime_t metadata_latency_min;
>>> ktime_t metadata_latency_max;
>> --
>> Jeff Layton <jlayton@redhat.com>
>>
>
next prev parent reply other threads:[~2021-09-22 13:46 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-21 13:07 [PATCH v3 0/4] ceph: forward average read/write/metadata latency Venky Shankar
2021-09-21 13:07 ` [PATCH v3 1/4] ceph: use "struct ceph_timespec" for r/w/m latencies Venky Shankar
2021-09-21 13:07 ` [PATCH v3 2/4] ceph: track average/stdev r/w/m latency Venky Shankar
2021-09-22 12:17 ` Jeff Layton
2021-09-22 12:33 ` Venky Shankar
2021-09-22 13:44 ` Venky Shankar
2021-09-22 14:34 ` Xiubo Li
2021-09-22 14:37 ` Xiubo Li
2021-09-22 17:10 ` Venky Shankar
2021-09-22 13:45 ` Xiubo Li [this message]
2021-09-21 13:07 ` [PATCH v3 3/4] ceph: include average/stddev r/w/m latency in mds metrics Venky Shankar
2021-09-21 13:07 ` [PATCH v3 4/4] ceph: use tracked average r/w/m latencies to display metrics in debugfs Venky Shankar
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