On Thu, Jan 31, 2019 at 5:33 PM Javier González <javier@xxxxxxxxxxx> wrote: > > > > > On 31 Jan 2019, at 11.41, Hans Holmberg <hans@xxxxxxxxxxxxx> wrote: > > > > Hi Javier! > > > > How did you test this? I'm trying to add a test case to our testing framework. > > > > This is what i ran in qemu, and I got a hang (with this version of the patch) > > > > nvme lnvm create -d nvme0n1 -t pblk -n pblk0 -f -b 0 -e 0 > > I run several low configurations without problem. Can you share the qemu configuration and version? > Of course! qemu remote: https://github.com/CNEX-Labs/qemu-nvme.git branch: master (cb200e3ccf9c1ff21f6275c6cb68b2801135a640) My geometry: parallel units: 8, secs per chk: 768, meta size 16, ws min 12, ws opt 24, cunits=0 > I’m on travel until Friday - I’ll come back to you over the weekend. Oh, no worries. This patch did not introduce the issue, so it's not a regression, but it looks like the same type of hang as the patch addresses. I might have stumbled across another bug. One thing I noticed was that the dd write block size that triggered the hang is >= write buffer. (128 entries * 4k) Safe travels! > > > > > kernel log: [ 116.381799] pblk pblk0: luns:1, lines:280, secs:212736, > > buf entries:128 > > > > # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=4k count=1 > > 1+0 records in > > 1+0 records out > > 4096 bytes (4.1 kB, 4.0 KiB) copied, 0.000480941 s, 8.5 MB/s > > # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=64k count=1 > > 1+0 records in > > 1+0 records out > > 65536 bytes (66 kB, 64 KiB) copied, 0.000477373 s, 137 MB/s > > # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=128k count=1 > > 1+0 records in > > 1+0 records out > > 131072 bytes (131 kB, 128 KiB) copied, 0.000548722 s, 239 MB/s > > # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=256k count=1 > > 1+0 records in > > 1+0 records out > > 262144 bytes (262 kB, 256 KiB) copied, 0.000718515 s, 365 MB/s > > # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=512k count=1 > > <HANG> > > > > > > > >> On Wed, Jan 30, 2019 at 11:28 AM Javier González <javier@xxxxxxxxxxx> wrote: > >> > >> In order to respect mw_cuinits, pblk's write buffer maintains a > >> backpointer to protect data not yet persisted; when writing to the write > >> buffer, this backpointer defines a threshold that pblk's rate-limiter > >> enforces. > >> > >> On small PU configurations, the following scenarios might take place: (i) > >> the threshold is larger than the write buffer and (ii) the threshold is > >> smaller than the write buffer, but larger than the maximun allowed > >> split bio - 256KB at this moment (Note that writes are not always > >> split - we only do this when we the size of the buffer is smaller > >> than the buffer). In both cases, pblk's rate-limiter prevents the I/O to > >> be written to the buffer, thus stalling. > >> > >> This patch fixes the original backpointer implementation by considering > >> the threshold both on buffer creation and on the rate-limiters path, > >> when bio_split is triggered (case (ii) above). > >> > >> Fixes: 766c8ceb16fc ("lightnvm: pblk: guarantee that backpointer is respected on writer stall") > >> Signed-off-by: Javier González <javier@xxxxxxxxxxx> > >> --- > >> > >> Changes since V1: > >> - Fix a bad arithmetinc on the rate-limiter max_io calculation (from > >> Hans) > >> > >> drivers/lightnvm/pblk-rb.c | 25 +++++++++++++++++++------ > >> drivers/lightnvm/pblk-rl.c | 5 ++--- > >> drivers/lightnvm/pblk.h | 2 +- > >> 3 files changed, 22 insertions(+), 10 deletions(-) > >> > >> diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c > >> index d4ca8c64ee0f..a6133b50ed9c 100644 > >> --- a/drivers/lightnvm/pblk-rb.c > >> +++ b/drivers/lightnvm/pblk-rb.c > >> @@ -45,10 +45,23 @@ void pblk_rb_free(struct pblk_rb *rb) > >> /* > >> * pblk_rb_calculate_size -- calculate the size of the write buffer > >> */ > >> -static unsigned int pblk_rb_calculate_size(unsigned int nr_entries) > >> +static unsigned int pblk_rb_calculate_size(unsigned int nr_entries, > >> + unsigned int threshold) > >> { > >> - /* Alloc a write buffer that can at least fit 128 entries */ > >> - return (1 << max(get_count_order(nr_entries), 7)); > >> + unsigned int thr_sz = 1 << (get_count_order(threshold + NVM_MAX_VLBA)); > >> + unsigned int max_sz = max(thr_sz, nr_entries); > >> + unsigned int max_io; > >> + > >> + /* Alloc a write buffer that can (i) fit at least two split bios > >> + * (considering max I/O size NVM_MAX_VLBA, and (ii) guarantee that the > >> + * threshold will be respected > >> + */ > >> + max_io = (1 << max((int)(get_count_order(max_sz)), > >> + (int)(get_count_order(NVM_MAX_VLBA << 1)))); > >> + if ((threshold + NVM_MAX_VLBA) >= max_io) > >> + max_io <<= 1; > >> + > >> + return max_io; > >> } > >> > >> /* > >> @@ -67,12 +80,12 @@ int pblk_rb_init(struct pblk_rb *rb, unsigned int size, unsigned int threshold, > >> unsigned int alloc_order, order, iter; > >> unsigned int nr_entries; > >> > >> - nr_entries = pblk_rb_calculate_size(size); > >> + nr_entries = pblk_rb_calculate_size(size, threshold); > >> entries = vzalloc(array_size(nr_entries, sizeof(struct pblk_rb_entry))); > >> if (!entries) > >> return -ENOMEM; > >> > >> - power_size = get_count_order(size); > >> + power_size = get_count_order(nr_entries); > >> power_seg_sz = get_count_order(seg_size); > >> > >> down_write(&pblk_rb_lock); > >> @@ -149,7 +162,7 @@ int pblk_rb_init(struct pblk_rb *rb, unsigned int size, unsigned int threshold, > >> * Initialize rate-limiter, which controls access to the write buffer > >> * by user and GC I/O > >> */ > >> - pblk_rl_init(&pblk->rl, rb->nr_entries); > >> + pblk_rl_init(&pblk->rl, rb->nr_entries, threshold); > >> > >> return 0; > >> } > >> diff --git a/drivers/lightnvm/pblk-rl.c b/drivers/lightnvm/pblk-rl.c > >> index 76116d5f78e4..e9e0af0df165 100644 > >> --- a/drivers/lightnvm/pblk-rl.c > >> +++ b/drivers/lightnvm/pblk-rl.c > >> @@ -207,7 +207,7 @@ void pblk_rl_free(struct pblk_rl *rl) > >> del_timer(&rl->u_timer); > >> } > >> > >> -void pblk_rl_init(struct pblk_rl *rl, int budget) > >> +void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold) > >> { > >> struct pblk *pblk = container_of(rl, struct pblk, rl); > >> struct nvm_tgt_dev *dev = pblk->dev; > >> @@ -217,7 +217,6 @@ void pblk_rl_init(struct pblk_rl *rl, int budget) > >> int sec_meta, blk_meta; > >> unsigned int rb_windows; > >> > >> - > >> /* Consider sectors used for metadata */ > >> sec_meta = (lm->smeta_sec + lm->emeta_sec[0]) * l_mg->nr_free_lines; > >> blk_meta = DIV_ROUND_UP(sec_meta, geo->clba); > >> @@ -234,7 +233,7 @@ void pblk_rl_init(struct pblk_rl *rl, int budget) > >> /* To start with, all buffer is available to user I/O writers */ > >> rl->rb_budget = budget; > >> rl->rb_user_max = budget; > >> - rl->rb_max_io = budget >> 1; > >> + rl->rb_max_io = budget - threshold; > >> rl->rb_gc_max = 0; > >> rl->rb_state = PBLK_RL_HIGH; > >> > >> diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h > >> index 72ae8755764e..a6386d5acd73 100644 > >> --- a/drivers/lightnvm/pblk.h > >> +++ b/drivers/lightnvm/pblk.h > >> @@ -924,7 +924,7 @@ int pblk_gc_sysfs_force(struct pblk *pblk, int force); > >> /* > >> * pblk rate limiter > >> */ > >> -void pblk_rl_init(struct pblk_rl *rl, int budget); > >> +void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold); > >> void pblk_rl_free(struct pblk_rl *rl); > >> void pblk_rl_update_rates(struct pblk_rl *rl); > >> int pblk_rl_high_thrs(struct pblk_rl *rl); > >> -- > >> 2.17.1 > >>
