On Sat, Apr 15, 2017 at 07:00:57AM -0700, Rodney W. Grimes wrote: > > On Fri, Apr 14, 2017 at 03:05:25PM -0700, Mark Johnston wrote: > > > > > > And with textdumps available, the benefit > > > > of having compression is limited because we can request for minidump > > > > or full dumps only when the textdumps are not good enough for > > > > diagnosing the kernel bug. > > > > > > Sure, but in this case the compression may be vital. > > > > > > > > > > > I don't think security (e.g. leaking information because of the use of > > > > compression) is a very big concern in this context because in order > > > > for the potential attacker to read the raw material needs a > > > > compromised system (unlike an attack from the network, where someone > > > > who controls the network would have access to the raw material); the > > > > dump is usually quite large, and measuring downtime would be hard at > > > > that scale. > > > > > > Ok. > > > > > > > > > > > By the way (not meant to bikeshed) if I was to do this I'd prefer > > > > using lz4 or something that compresses faster than zlib. > > > > > > I agree, but I think the existing lz4 implementation in the kernel is > > > not so well suited to running after a panic. It seems fixable, but > > > compression speed also isn't hugely important here IMO. > > > > On production system this is downtime. > > For may case, dumped about 32GB (from 256GB RAM). This is take several > > minutes. Can compression increase this to hour? > > On productions systems the compression layer of dump may very well > be a win situation depending on choosen algorith (you want something > fairly fast, but still effective). If your rate to compress bytes > is close to the disk write bandwith you have an over all win caused > by writting less to disk. > > Someone who enjoys math should write an equation for given > compression bandwidth cb and given disk bandwidth db and > compression ratio cr what do the curves look like? > > IIRC we measure cpu/memory bandwidth in the 10'sG bytes/sec
wrong. single thread cpu/memory bandwidth very different on i7 and e5 cpu (e5 less, about 6 GB/s). > range, compression should be some place under that, and > our disk bandwidth even on SSD is in the 500MB range, > even the fastest 15k rpm spinning rust is in the <200MB > range, we should be able to compress at a higher rate than > this. yes. _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
