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From: "Dziegielewski, Marcin" <marcin.dziegielewski@intel.com>
To: Javier Gonzalez <javier@cnexlabs.com>
Cc: Matias Bjorling <mb@lightnvm.io>, Jens Axboe <axboe@fb.com>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Konopko, Igor J" <igor.j.konopko@intel.com>
Subject: RE: [GIT PULL 18/20] lightnvm: pblk: handle case when mw_cunits equals to 0
Date: Mon, 4 Jun 2018 17:17:53 +0000	[thread overview]
Message-ID: <9FC4315EA6BEAA449828D92CF173A10D3E38365C@IRSMSX109.ger.corp.intel.com> (raw)
In-Reply-To: <3A87DF02-6471-4B92-9DDC-4E0FD98249A4@cnexlabs.com>

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WARNING: multiple messages have this Message-ID (diff)
From: "Dziegielewski, Marcin" <marcin.dziegielewski@intel.com>
To: Javier Gonzalez <javier@cnexlabs.com>
Cc: Matias Bjorling <mb@lightnvm.io>, Jens Axboe <axboe@fb.com>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Konopko, Igor J" <igor.j.konopko@intel.com>
Subject: RE: [GIT PULL 18/20] lightnvm: pblk: handle case when mw_cunits equals to 0
Date: Mon, 4 Jun 2018 17:17:53 +0000	[thread overview]
Message-ID: <9FC4315EA6BEAA449828D92CF173A10D3E38365C@IRSMSX109.ger.corp.intel.com> (raw)
In-Reply-To: <3A87DF02-6471-4B92-9DDC-4E0FD98249A4@cnexlabs.com>

> From: Javier Gonzalez [mailto:javier@cnexlabs.com]
> Sent: Monday, June 4, 2018 1:16 PM
> To: Dziegielewski, Marcin <marcin.dziegielewski@intel.com>
> Cc: Matias Bjørling <mb@lightnvm.io>; Jens Axboe <axboe@fb.com>; linux-
> block@vger.kernel.org; linux-kernel@vger.kernel.org; Konopko, Igor J
> <igor.j.konopko@intel.com>
> 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@intel.com> wrote:
> >
> >> -----Original Message-----
> >> From: Javier Gonzalez [mailto:javier@cnexlabs.com]
> >> Sent: Monday, June 4, 2018 12:22 PM
> >> To: Dziegielewski, Marcin <marcin.dziegielewski@intel.com>
> >> Cc: Matias Bjørling <mb@lightnvm.io>; Jens Axboe <axboe@fb.com>;
> >> linux- block@vger.kernel.org; linux-kernel@vger.kernel.org; Konopko,
> >> Igor J <igor.j.konopko@intel.com>
> >> 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@intel.com> wrote:
> >>> Frist of all I want to say sorry for late response - I was on holiday.
> >>>
> >>>> From: Javier Gonzalez [mailto:javier@cnexlabs.com]
> >>>> Sent: Monday, May 28, 2018 1:03 PM
> >>>> To: Matias Bjørling <mb@lightnvm.io>
> >>>> Cc: Jens Axboe <axboe@fb.com>; linux-block@vger.kernel.org; linux-
> >>>> kernel@vger.kernel.org; Dziegielewski, Marcin
> >>>> <marcin.dziegielewski@intel.com>; Konopko, Igor J
> >>>> <igor.j.konopko@intel.com>
> >>>> 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@lightnvm.io> wrote:
> >>>>>
> >>>>> From: Marcin Dziegielewski <marcin.dziegielewski@intel.com>
> >>>>>
> >>>>> 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@intel.com>
> >>>>> Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
> >>>>> Signed-off-by: Matias Bjørling <mb@lightnvm.io>
> >>>>> ---
> >>>>> 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.

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.

> 
> >
> >>>> Javier
> >>>
> >>> Thanks,
> >>> Marcin
> >>
> >> Javier
> > Thanks,
> > Marcin
Thanks!,
Marcin

  reply	other threads:[~2018-06-04 17:17 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-28  8:58 [GIT PULL 00/20] lightnvm updates for 4.18 Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 01/20] lightnvm: pblk: fail gracefully on line alloc. failure Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 02/20] lightnvm: pblk: recheck for bad lines at runtime Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 03/20] lightnvm: pblk: check read lba on gc path Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 04/20] lightnvm: pblk: improve error msg on corrupted LBAs Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 05/20] lightnvm: pblk: warn in case of corrupted write buffer Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 06/20] lightnvm: pblk: return NVM_ error on failed submission Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 07/20] lightnvm: pblk: remove unnecessary indirection Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 08/20] lightnvm: pblk: remove unnecessary argument Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 09/20] lightnvm: pblk: check for chunk size before allocating it Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 10/20] lightnvm: pass flag on graceful teardown to targets Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 11/20] lightnvm: pblk: remove dead function Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 12/20] lightnvm: pblk: rework write error recovery path Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 13/20] lightnvm: pblk: garbage collect lines with failed writes Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 14/20] lightnvm: pblk: fix smeta write error path Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 15/20] lightnvm: proper error handling for pblk_bio_add_pages Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 16/20] lightnvm: error handling when whole line is bad Matias Bjørling
2018-05-28 10:59   ` Javier Gonzalez
2018-05-29 13:15     ` Konopko, Igor J
2018-05-29 18:29       ` Javier Gonzalez
2018-05-28  8:58 ` [GIT PULL 17/20] lightnvm: fix partial read error path Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 18/20] lightnvm: pblk: handle case when mw_cunits equals to 0 Matias Bjørling
2018-05-28 11:02   ` Javier Gonzalez
2018-06-04 10:09     ` Dziegielewski, Marcin
2018-06-04 10:09       ` Dziegielewski, Marcin
2018-06-04 10:21       ` Javier Gonzalez
2018-06-04 10:21         ` Javier Gonzalez
2018-06-04 11:11         ` Dziegielewski, Marcin
2018-06-04 11:11           ` Dziegielewski, Marcin
2018-06-04 11:15           ` Javier Gonzalez
2018-06-04 11:15             ` Javier Gonzalez
2018-06-04 17:17             ` Dziegielewski, Marcin [this message]
2018-06-04 17:17               ` Dziegielewski, Marcin
2018-06-05  7:12               ` Javier Gonzalez
2018-06-05  9:18                 ` Dziegielewski, Marcin
2018-05-28  8:58 ` [GIT PULL 19/20] lightnvm: pblk: add possibility to set write buffer size manually Matias Bjørling
2018-05-28  8:58 ` [GIT PULL 20/20] lightnvm: pblk: sync RB and RL states during GC Matias Bjørling
2018-05-28 10:51   ` Javier Gonzalez
2018-05-29 13:07     ` Konopko, Igor J
2018-05-29 17:58       ` Javier Gonzalez
2018-06-01 10:45 ` [GIT PULL 00/20] lightnvm updates for 4.18 Matias Bjørling
2018-06-01 12:36   ` Jens Axboe
2018-06-01 12:36     ` Jens Axboe

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