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 ?. 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. > > 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? > > Javier Thanks, Marcin
