Messages in this thread | | | Subject | Re: [PATCH 4/5] lightnvm: pblk: add padding distribution sysfs attribute | From | Matias Bjørling <> | Date | Wed, 31 Jan 2018 09:44:52 +0100 |
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On 01/31/2018 03:06 AM, Javier González wrote: > From: Hans Holmberg <hans.holmberg@cnexlabs.com> > > When pblk receives a sync, all data up to that point in the write buffer > must be comitted to persistent storage, and as flash memory comes with a > minimal write size there is a significant cost involved both in terms > of time for completing the sync and in terms of write amplification > padded sectors for filling up to the minimal write size. > > In order to get a better understanding of the costs involved for syncs, > Add a sysfs attribute to pblk: padded_dist, showing a normalized > distribution of sectors padded. In order to facilitate measurements of > specific workloads during the lifetime of the pblk instance, the > distribution can be reset by writing 0 to the attribute. > > Do this by introducing counters for each possible padding: > {0..(minimal write size - 1)} and calculate the normalized distribution > when showing the attribute. > > Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com> > Signed-off-by: Javier González <javier@cnexlabs.com> > --- > drivers/lightnvm/pblk-init.c | 16 ++++++++-- > drivers/lightnvm/pblk-rb.c | 15 +++++----- > drivers/lightnvm/pblk-sysfs.c | 68 +++++++++++++++++++++++++++++++++++++++++++ > drivers/lightnvm/pblk.h | 6 +++- > 4 files changed, 95 insertions(+), 10 deletions(-) > > diff --git a/drivers/lightnvm/pblk-init.c b/drivers/lightnvm/pblk-init.c > index 7eedc5daebc8..a5e3510c0f38 100644 > --- a/drivers/lightnvm/pblk-init.c > +++ b/drivers/lightnvm/pblk-init.c > @@ -921,6 +921,7 @@ static void pblk_free(struct pblk *pblk) > { > pblk_luns_free(pblk); > pblk_lines_free(pblk); > + kfree(pblk->pad_dist); > pblk_line_meta_free(pblk); > pblk_core_free(pblk); > pblk_l2p_free(pblk); > @@ -998,11 +999,13 @@ static void *pblk_init(struct nvm_tgt_dev *dev, struct gendisk *tdisk, > pblk->pad_rst_wa = 0; > pblk->gc_rst_wa = 0; > > + atomic_long_set(&pblk->nr_flush, 0); > + pblk->nr_flush_rst = 0; > + > #ifdef CONFIG_NVM_DEBUG > atomic_long_set(&pblk->inflight_writes, 0); > atomic_long_set(&pblk->padded_writes, 0); > atomic_long_set(&pblk->padded_wb, 0); > - atomic_long_set(&pblk->nr_flush, 0); > atomic_long_set(&pblk->req_writes, 0); > atomic_long_set(&pblk->sub_writes, 0); > atomic_long_set(&pblk->sync_writes, 0); > @@ -1034,10 +1037,17 @@ static void *pblk_init(struct nvm_tgt_dev *dev, struct gendisk *tdisk, > goto fail_free_luns; > } > > + pblk->pad_dist = kzalloc((pblk->min_write_pgs - 1) * sizeof(atomic64_t), > + GFP_KERNEL); > + if (!pblk->pad_dist) { > + ret = -ENOMEM; > + goto fail_free_line_meta; > + } > + > ret = pblk_core_init(pblk); > if (ret) { > pr_err("pblk: could not initialize core\n"); > - goto fail_free_line_meta; > + goto fail_free_pad_dist; > } > > ret = pblk_l2p_init(pblk); > @@ -1097,6 +1107,8 @@ static void *pblk_init(struct nvm_tgt_dev *dev, struct gendisk *tdisk, > pblk_l2p_free(pblk); > fail_free_core: > pblk_core_free(pblk); > +fail_free_pad_dist: > + kfree(pblk->pad_dist); > fail_free_line_meta: > pblk_line_meta_free(pblk); > fail_free_luns: > diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c > index 7044b5599cc4..264372d7b537 100644 > --- a/drivers/lightnvm/pblk-rb.c > +++ b/drivers/lightnvm/pblk-rb.c > @@ -437,9 +437,7 @@ static int pblk_rb_may_write_flush(struct pblk_rb *rb, unsigned int nr_entries, > if (bio->bi_opf & REQ_PREFLUSH) { > struct pblk *pblk = container_of(rb, struct pblk, rwb); > > -#ifdef CONFIG_NVM_DEBUG > atomic_long_inc(&pblk->nr_flush); > -#endif > if (pblk_rb_flush_point_set(&pblk->rwb, bio, mem)) > *io_ret = NVM_IO_OK; > } > @@ -620,14 +618,17 @@ unsigned int pblk_rb_read_to_bio(struct pblk_rb *rb, struct nvm_rq *rqd, > pr_err("pblk: could not pad page in write bio\n"); > return NVM_IO_ERR; > } > + > + if (pad < pblk->min_write_pgs) > + atomic64_inc(&pblk->pad_dist[pad - 1]); > + else > + pr_warn("pblk: padding more than min. sectors\n");
Curious, when would this happen? Would it be an implementation error or something a user did wrong?
> + > + atomic64_add(pad, &pblk->pad_wa); > } > > - atomic64_add(pad, &((struct pblk *) > - (container_of(rb, struct pblk, rwb)))->pad_wa); > - > #ifdef CONFIG_NVM_DEBUG > - atomic_long_add(pad, &((struct pblk *) > - (container_of(rb, struct pblk, rwb)))->padded_writes); > + atomic_long_add(pad, &pblk->padded_writes); > #endif > > return NVM_IO_OK; > diff --git a/drivers/lightnvm/pblk-sysfs.c b/drivers/lightnvm/pblk-sysfs.c > index 4804bbd32d5f..f902ac00d071 100644 > --- a/drivers/lightnvm/pblk-sysfs.c > +++ b/drivers/lightnvm/pblk-sysfs.c > @@ -341,6 +341,38 @@ static ssize_t pblk_sysfs_get_write_amp_trip(struct pblk *pblk, char *page) > atomic64_read(&pblk->pad_wa) - pblk->pad_rst_wa, page); > } > > +static ssize_t pblk_sysfs_get_padding_dist(struct pblk *pblk, char *page) > +{ > + int sz = 0; > + unsigned long long total; > + unsigned long long total_buckets = 0; > + int buckets = pblk->min_write_pgs - 1; > + int i; > + > + total = atomic64_read(&pblk->nr_flush) - pblk->nr_flush_rst; > + > + for (i = 0; i < buckets; i++) > + total_buckets += atomic64_read(&pblk->pad_dist[i]); > +
total_buckets are first used later. The calculation could be moved below the next statement.
> + if (!total) { > + for (i = 0; i < (buckets + 1); i++) > + sz += snprintf(page + sz, PAGE_SIZE - sz, > + "%d:0 ", i); > + sz += snprintf(page + sz, PAGE_SIZE - sz, "\n"); > + > + return sz; > + } > + > + sz += snprintf(page + sz, PAGE_SIZE - sz, "0:%lld%% ", > + ((total - total_buckets) * 100) / total); > + for (i = 0; i < buckets; i++) > + sz += snprintf(page + sz, PAGE_SIZE - sz, "%d:%lld%% ", i + 1, > + (atomic64_read(&pblk->pad_dist[i]) * 100) / total); > + sz += snprintf(page + sz, PAGE_SIZE - sz, "\n"); > + > + return sz; > +} > + > #ifdef CONFIG_NVM_DEBUG > static ssize_t pblk_sysfs_stats_debug(struct pblk *pblk, char *page) > { > @@ -427,6 +459,32 @@ static ssize_t pblk_sysfs_set_write_amp_trip(struct pblk *pblk, > } > > > +static ssize_t pblk_sysfs_set_padding_dist(struct pblk *pblk, > + const char *page, size_t len) > +{ > + size_t c_len; > + int reset_value; > + int buckets = pblk->min_write_pgs - 1; > + int i; > + > + c_len = strcspn(page, "\n"); > + if (c_len >= len) > + return -EINVAL; > + > + if (kstrtouint(page, 0, &reset_value)) > + return -EINVAL; > + > + if (reset_value != 0) > + return -EINVAL; > + > + for (i = 0; i < buckets; i++) > + atomic64_set(&pblk->pad_dist[i], 0); > + > + pblk->nr_flush_rst = atomic64_read(&pblk->nr_flush); > + > + return len; > +} > + > static struct attribute sys_write_luns = { > .name = "write_luns", > .mode = 0444, > @@ -487,6 +545,11 @@ static struct attribute sys_write_amp_trip = { > .mode = 0644, > }; > > +static struct attribute sys_padding_dist = { > + .name = "padding_dist", > + .mode = 0644, > +}; > + > #ifdef CONFIG_NVM_DEBUG > static struct attribute sys_stats_debug_attr = { > .name = "stats", > @@ -507,6 +570,7 @@ static struct attribute *pblk_attrs[] = { > &sys_lines_info_attr, > &sys_write_amp_mileage, > &sys_write_amp_trip, > + &sys_padding_dist, > #ifdef CONFIG_NVM_DEBUG > &sys_stats_debug_attr, > #endif > @@ -540,6 +604,8 @@ static ssize_t pblk_sysfs_show(struct kobject *kobj, struct attribute *attr, > return pblk_sysfs_get_write_amp_mileage(pblk, buf); > else if (strcmp(attr->name, "write_amp_trip") == 0) > return pblk_sysfs_get_write_amp_trip(pblk, buf); > + else if (strcmp(attr->name, "padding_dist") == 0) > + return pblk_sysfs_get_padding_dist(pblk, buf); > #ifdef CONFIG_NVM_DEBUG > else if (strcmp(attr->name, "stats") == 0) > return pblk_sysfs_stats_debug(pblk, buf); > @@ -558,6 +624,8 @@ static ssize_t pblk_sysfs_store(struct kobject *kobj, struct attribute *attr, > return pblk_sysfs_set_sec_per_write(pblk, buf, len); > else if (strcmp(attr->name, "write_amp_trip") == 0) > return pblk_sysfs_set_write_amp_trip(pblk, buf, len); > + else if (strcmp(attr->name, "padding_dist") == 0) > + return pblk_sysfs_set_padding_dist(pblk, buf, len); > return 0; > } > > diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h > index 4b7d8618631f..88720e2441c0 100644 > --- a/drivers/lightnvm/pblk.h > +++ b/drivers/lightnvm/pblk.h > @@ -626,12 +626,16 @@ struct pblk { > u64 gc_rst_wa; > u64 pad_rst_wa; > > + /* Counters used for calculating padding distribution */ > + atomic64_t *pad_dist; /* Padding distribution buckets */ > + u64 nr_flush_rst; /* Flushes reset value for pad dist.*/ > + atomic_long_t nr_flush; /* Number of flush/fua I/O */ > + > #ifdef CONFIG_NVM_DEBUG > /* Non-persistent debug counters, 4kb sector I/Os */ > atomic_long_t inflight_writes; /* Inflight writes (user and gc) */ > atomic_long_t padded_writes; /* Sectors padded due to flush/fua */ > atomic_long_t padded_wb; /* Sectors padded in write buffer */ > - atomic_long_t nr_flush; /* Number of flush/fua I/O */ > atomic_long_t req_writes; /* Sectors stored on write buffer */ > atomic_long_t sub_writes; /* Sectors submitted from buffer */ > atomic_long_t sync_writes; /* Sectors synced to media */ >
Looks good to me. Let me know if you want to send a new patch, or if I may make the change when I pick it up.
Also, should the padding be stored in the on-disk metadata as well?
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