*ping* Any word on my previous counter-proposal? Shall I prepare another patch for consideration? -san On Thu, Apr 22, 2010 at 12:42 PM, San Mehat <san@xxxxxxxxxx> wrote: > On Thu, Apr 22, 2010 at 11:47 AM, Milan Broz <mbroz@xxxxxxxxxx> wrote: >> On 04/22/2010 08:08 PM, San Mehat wrote: >>> On Thu, Apr 22, 2010 at 11:03 AM, Milan Broz <mbroz@xxxxxxxxxx> wrote: >>>> On 04/22/2010 07:48 PM, San Mehat wrote: >>>>> Typically, dm-crypt instances each have their own set of kcrypt/kcrypt_io >>>>> work-queues. This patch adds an option which will create one set of >>>>> work-queues on init, and re-uses them for all dm-crypt target instances. >> >>>> Can you explain the real reason for this patch? >>>> >>> >>> Sure, I'd be happy to explain. >> >> (Please add this always to patch header.) >> > > Will do - thanks. > >>> >>> Upcoming versions of android are about to start using dm/dm-crypt >>> heavily, having >>> a large number of small dm-crypt instances running on the device (hard >>> to tell just >>> how many, but i've seen cases where up to 50 or 60 instances may be >>> running). This ends up creating 100 - 120 kernel threads, and I was >>> simply trying to cut that down. >> >> Sorry, but I don't take this argument. "Too many notes!" :-) >> >> So the problem is with memory allocation? Scheduler? Or where? >> Kernel threads should be cheap. >> > > Well the initial consideration was towards memory overhead with so > many threads that don't do much (in our use-case) on an embedded > device. > >> If you need 60 crypt devices, you almost surely hit at least starvation >> problem with one global queue! >> (Just curious - what are these crypt devices doing?) > > The crypt devices are providing small read-only encrypted file-systems > - whose backing files exist on an external FAT file-system, and are > created on-demand as needed. In this usage scenario, we'll only see > typically a few of these devices being simultaneously accessed, (and > the sd-card throughput is definitely the long-pole in the performance > profile, so even when I beat on 80 or 90 concurrent instances, we're > mainly waiting for mmcqd to complete transactions). > >> >>> I'd be more than happy to discuss alternatives; but do we *really* >>> need 2 work-queue threads per instance? >> >> yes. > > What if we made a note in the Kconfig advising against using the option in > stacked configurations? (Or even make it depend on CONFIG_EMBEDDED) > > Thanks for your time, > > -san > >> >> For separate io queue - see commit cabf08e4d3d1181d7c408edae97fb4d1c31518af >> >> | Add post-processing queue (per crypt device) for read operations. >> >> | Current implementation uses only one queue for all operations >> | and this can lead to starvation caused by many requests waiting >> | for memory allocation. But the needed memory-releasing operation >> | is queued after these requests (in the same queue). >> >> >> (and there were another problem with async crypt - callback is called >> in interrupt context, bio must be submitted from separate workqueue IIRC) >> >>>> (cc: Alasdair - I think he will not accept the patch anyway.) >>> >>> Probably not, but at least we can get the discussion going :) >> >> I am not saying that I do not want to discuss this - but we must know >> the real problems many queues are causing first. >> And then think about possible solutions. >> >> Milan >> > > > > -- > San Mehat | Staff Software Engineer | Android | Google Inc. > 415.366.6172 (san@xxxxxxxxxx) > -- San Mehat | Staff Software Engineer | Android | Google Inc. 415.366.6172 (san@xxxxxxxxxx) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel