> -----Original Message----- > From: Bartlomiej Zolnierkiewicz [mailto:b.zolnier...@samsung.com] > Sent: Tuesday, October 01, 2013 10:01 PM > To: Ramprasad C > Cc: ax...@kernel.dk; Akhil Bhansali; jmo...@redhat.com; > kyungmin.p...@samsung.com; linux-kernel@vger.kernel.org; OS > Engineering; Amit Phansalkar > Subject: Re: [PATCH 14/14] skd: remove skd_bio code > > > Hi Ramprasad, > > On Tuesday, October 01, 2013 06:46:00 PM Ramprasad C wrote: > > Hi Bartlomiej, > > > > Thank for your contributions to skd driver. > > > > The reason why skd driver has two code paths is:- > > 1. For some workloads, Bio code path (skd_bio=1) performs better as > > compared to default code, like random r/w, high queue depths, direct > i/o > > etc. In Bio code path, driver bypasses linux block elevator + > scheduler > > layers and 'struct bio' comes directly to driver through > make_request_fn(). > > Have you tried using "noop" I/O scheduler to alleviate the issue? > > You need the kernel compiled with CONFIG_IOSCHED_NOOP=y (it is enabled > by > default) and then do i.e. "echo noop > /sys/block/skd0/queue/scheduler" > to > enable "noop" I/O scheduler for the skd0 block device. > > > 2. For some workloads like buffered mode (app) i/o, the default code > path > > performs much better. Hence, both the code paths are kept with module > > parameter. We would prefer to have both code paths. > > It would be very useful to see some numbers for skd_bio=1 and skd_bio=0 > (with "noop" I/O scheduler enabled) for the affected workloads to see > what > kind of improvement is offered by skd_bio=1. > > If the block layer queuing code is a problem even with "noop" I/O > scheduler > it would be much better try to identify and fix (if possible) the > problem > parts in the generic block layer code. This would benefit all SSD > hardware > used on Linux not only the one supported by skd driver. > > Also it is very inflexible to require the driver re-load just to > optimize > it for some workload. I believe that a better solution (runtime > selection > of the mode of operation at the block layer level) can be provided if > really necessary. >
Hi Bartlomiej, There was performance gap with noop too. However, for noop with nomerge=1 and rotation=0, the performance difference is marginal. We feel the skd_bio=1 code path can be removed and can keep the single (default) code path in the driver. Regards, Ramprasad > Best regards, > -- > Bartlomiej Zolnierkiewicz > Samsung R&D Institute Poland > Samsung Electronics > > > Regards, > > Ramprasad > > > > > > > > On Mon, Sep 30, 2013 at 6:55 PM, Bartlomiej Zolnierkiewicz < > > b.zolnier...@samsung.com> wrote: > > > > > skd_bio feature adds a possibility to use the internal bio list to > process > > > requests instead of using the normal block layer queueing > functionality. > > > Its potential advantages are unclear and if there are any it is > better to > > > identify and fix the block layer code deficiences instead. Moreover > it > > > introduces separate code-paths through the whole driver which are > difficult > > > to test properly and maintain in the long-term. Since it is > currently not > > > used unless explicitly enabled by module parameter just remove it. > > > > > > Cc: Akhil Bhansali <abhans...@stec-inc.com> > > > Cc: Jeff Moyer <jmo...@redhat.com> > > > Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnier...@samsung.com> > > > Signed-off-by: Kyungmin Park <kyungmin.p...@samsung.com> > > > --- > > > drivers/block/skd_main.c | 605 > > > ++++++----------------------------------------- > > > 1 file changed, 76 insertions(+), 529 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
