> On 4 Jun 2018, at 19.17, Dziegielewski, Marcin <marcin.dziegielewski@xxxxxxxxx> wrote: > >> From: Javier Gonzalez [mailto:javier@xxxxxxxxxxxx] >> Sent: Monday, June 4, 2018 1:16 PM >> To: Dziegielewski, Marcin <marcin.dziegielewski@xxxxxxxxx> >> Cc: Matias Bjørling <mb@xxxxxxxxxxx>; Jens Axboe <axboe@xxxxxx>; linux- >> block@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Konopko, Igor J >> <igor.j.konopko@xxxxxxxxx> >> Subject: Re: [GIT PULL 18/20] lightnvm: pblk: handle case when mw_cunits >> equals to 0 >> >> >>> On 4 Jun 2018, at 13.11, Dziegielewski, Marcin >> <marcin.dziegielewski@xxxxxxxxx> wrote: >>>> -----Original Message----- >>>> From: Javier Gonzalez [mailto:javier@xxxxxxxxxxxx] >>>> Sent: Monday, June 4, 2018 12:22 PM >>>> To: Dziegielewski, Marcin <marcin.dziegielewski@xxxxxxxxx> >>>> Cc: Matias Bjørling <mb@xxxxxxxxxxx>; Jens Axboe <axboe@xxxxxx>; >>>> linux- block@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Konopko, >>>> Igor J <igor.j.konopko@xxxxxxxxx> >>>> Subject: Re: [GIT PULL 18/20] lightnvm: pblk: handle case when >>>> mw_cunits equals to 0 >>>> >>>>> On 4 Jun 2018, at 12.09, Dziegielewski, Marcin >>>> <marcin.dziegielewski@xxxxxxxxx> wrote: >>>>> Frist of all I want to say sorry for late response - I was on holiday. >>>>> >>>>>> From: Javier Gonzalez [mailto:javier@xxxxxxxxxxxx] >>>>>> Sent: Monday, May 28, 2018 1:03 PM >>>>>> To: Matias Bjørling <mb@xxxxxxxxxxx> >>>>>> Cc: Jens Axboe <axboe@xxxxxx>; linux-block@xxxxxxxxxxxxxxx; linux- >>>>>> kernel@xxxxxxxxxxxxxxx; Dziegielewski, Marcin >>>>>> <marcin.dziegielewski@xxxxxxxxx>; Konopko, Igor J >>>>>> <igor.j.konopko@xxxxxxxxx> >>>>>> Subject: Re: [GIT PULL 18/20] lightnvm: pblk: handle case when >>>>>> mw_cunits equals to 0 >>>>>> >>>>>>> On 28 May 2018, at 10.58, Matias Bjørling <mb@xxxxxxxxxxx> wrote: >>>>>>> >>>>>>> From: Marcin Dziegielewski <marcin.dziegielewski@xxxxxxxxx> >>>>>>> >>>>>>> Some devices can expose mw_cunits equal to 0, it can cause >>>>>>> creation of too small write buffer and cause performance to drop >>>>>>> on write workloads. >>>>>>> >>>>>>> To handle that, we use the default value for MLC and beacause it >>>>>>> covers both 1.2 and 2.0 OC specification, setting up mw_cunits in >>>>>>> nvme_nvm_setup_12 function isn't longer necessary. >>>>>>> >>>>>>> Signed-off-by: Marcin Dziegielewski >>>>>>> <marcin.dziegielewski@xxxxxxxxx> >>>>>>> Signed-off-by: Igor Konopko <igor.j.konopko@xxxxxxxxx> >>>>>>> Signed-off-by: Matias Bjørling <mb@xxxxxxxxxxx> >>>>>>> --- >>>>>>> drivers/lightnvm/pblk-init.c | 10 +++++++++- >>>>>>> drivers/nvme/host/lightnvm.c | 1 - >>>>>>> 2 files changed, 9 insertions(+), 2 deletions(-) >>>>>>> >>>>>>> diff --git a/drivers/lightnvm/pblk-init.c >>>>>>> b/drivers/lightnvm/pblk-init.c index d65d2f972ccf..0f277744266b >>>>>>> 100644 >>>>>>> --- a/drivers/lightnvm/pblk-init.c >>>>>>> +++ b/drivers/lightnvm/pblk-init.c >>>>>>> @@ -356,7 +356,15 @@ static int pblk_core_init(struct pblk *pblk) >>>>>>> atomic64_set(&pblk->nr_flush, 0); >>>>>>> pblk->nr_flush_rst = 0; >>>>>>> >>>>>>> - pblk->pgs_in_buffer = geo->mw_cunits * geo->all_luns; >>>>>>> + if (geo->mw_cunits) { >>>>>>> + pblk->pgs_in_buffer = geo->mw_cunits * geo- >>> all_luns; >>>>>>> + } else { >>>>>>> + pblk->pgs_in_buffer = (geo->ws_opt << 3) * geo- >>> all_luns; >>>>>>> + /* >>>>>>> + * Some devices can expose mw_cunits equal to 0, so >> let's >>>>>> use >>>>>>> + * here default safe value for MLC. >>>>>>> + */ >>>>>>> + } >>>>>>> >>>>>>> pblk->min_write_pgs = geo->ws_opt * (geo->csecs / PAGE_SIZE); >>>>>>> max_write_ppas = pblk->min_write_pgs * geo->all_luns; diff --git >>>>>>> a/drivers/nvme/host/lightnvm.c b/drivers/nvme/host/lightnvm.c >>>>>>> index >>>>>>> 41279da799ed..c747792da915 100644 >>>>>>> --- a/drivers/nvme/host/lightnvm.c >>>>>>> +++ b/drivers/nvme/host/lightnvm.c >>>>>>> @@ -338,7 +338,6 @@ static int nvme_nvm_setup_12(struct >>>>>> nvme_nvm_id12 >>>>>>> *id, >>>>>>> >>>>>>> geo->ws_min = sec_per_pg; >>>>>>> geo->ws_opt = sec_per_pg; >>>>>>> - geo->mw_cunits = geo->ws_opt << 3; /* default to MLC >> safe values >>>>>> */ >>>>>>> /* Do not impose values for maximum number of open blocks as it is >>>>>>> * unspecified in 1.2. Users of 1.2 must be aware of this and >>>>>>> eventually >>>>>>> -- >>>>>>> 2.11.0 >>>>>> >>>>>> By doing this, 1.2 future users (beyond pblk), will fail to have a >>>>>> valid mw_cunits value. It's ok to deal with the 0 case in pblk, but >>>>>> I believe that we should have the default value for 1.2 either way. >>>>> >>>>> I'm not sure. From my understanding, setting of default value was >>>>> workaround for pblk case, am I right ?. >>>> >>>> The default value covers the MLC case directly at the lightnvm layer, >>>> as opposed to doing it directly in pblk. Since pblk is the only user >>>> now, you can argue that all changes in the lightnvm layer are to >>>> solve pblk issues, but the idea is that the geometry should be generic. >>>> >>>>> In my opinion any user of 1.2 >>>>> spec should be aware that there is not mw_cunit value. From my point >>>>> of view, leaving here 0 (and decision what do with it to lightnvm >>>>> user) is more safer way, but maybe I'm wrong. I believe that it is >>>>> topic to wider discussion with maintainers. >>>> >>>> 1.2 and 2.0 have different geometries, but when we designed the >>>> common nvm_geo structure, the idea was to abstract both specs and >>>> allow the upper layers to use the geometry transparently. >>>> >>>> Specifically in pblk, I would prefer to keep it in such a way that we >>>> don't need to media specific policies (e.g., set default values for >>>> MLC memories), as a general design principle. We already do some >>>> geometry version checks to avoid dereferencing unnecessary pointers >>>> on the fast path, which I would eventually like to remove. >>> >>> Ok, now I understand your point of view and agree with that, I will >>> prepare second version of this patch without this change. >> >> Sounds good. >> >>> Thanks for >>> the clarification. >> >> Sure :) >> >>>>>> A more generic way of doing this would be to have a default value >>>>>> for >>>>>> 2.0 too, in case mw_cunits is reported as 0. >>>>> >>>>> Since 0 is correct value and users can make different decisions >>>>> based on it, I think we shouldn't overwrite it by default value. Is >>>>> it make sense? >>>> >>>> Here I meant at a pblk level - I should have specified it. At the >>>> geometry level, we should not change it. >>>> >>>> The case I am thinking is if mw_cuints repoints 0, but ws_min > 0. In >>>> this case, we still need a host side buffer to serve < ws_min I/Os, >>>> even though the device does not require the buffer to guarantee reads. >>> >>> Oh, ok now we are on the same page. In this patch I was trying to >>> address such case. Do you have other idea how to do it or here are you >>> thinking only on value of default variable? >> >> If doing this, I guess that something in the line of what you did with >> increasing the size of the write buffer via a module parameter. For example, >> checking if the size of the write buffer based on mw_cuints is enough to >> cover ws_min, which normally would only be an issue when mw_cuints == 0 >> or when the number of PUs used for the pblk instance is very small and >> mw_cuints < nr_luns * ws_min. > > > I see here two cases: > - when mw_cunits > 0 buffer size should have number of entries at > least max(mw_cunits, ws_min) * nr_luns and here we are taking care of > both cases mw_cunits > ws_min and mw_cunits < ws_min. > - when mw_cunit == 0 buffer size should have number of entries at > least ws_min * nr _luns and we can use the same puseudocode as above. > Agree. > Do you see any other case? Could you clarify second case mentioned by > you or maybe did you mean opposite case? If yes, I believe that above > pseudo code will handle such case too. > Yes, it is the same case. One thing to consider is whether the buffer should at least be ws_opt * nr_luns for performance reasons. Since the write thread will always try to send ws_opt, in the case that ws_opt > ws_min, then a buffer size of ws_min * nr_luns will not make use of the whole parallelism exposed by the device. Therefore, I would probably go for ws_opt * nr_luns as the default value when mw_cuints * nr_luns < ws_opt * nr_luns (which covers mw_cuints == 0), and then keep ws_min * nr_luns as the minimum requirement when setting the buffer size manually. Does this cover your use case? >>>>>> Javier >>>>> >>>>> Thanks, >>>>> Marcin >>>> >>>> Javier >>> Thanks, >>> Marcin > Thanks!, > Marcin
