One more question, and hopefully I will not bug you further on this :-) How exactly do you parse the kernel parameters? I thought it would be plain simple, but seems like the command line string is not available to SCSI driver like ours, or I am missing something? Thanks -Atul -----Original Message----- From: Vivek Goyal [mailto:vgoyal@xxxxxxxxxx] Sent: Friday, September 21, 2007 12:15 AM To: Mukker, Atul Cc: Kexec Mailing List; Moore, Eric Subject: Re: kdump info request On Wed, Sep 19, 2007 at 07:26:19AM -0600, Mukker, Atul wrote: [..] > > > > If we could somehow determine that we are being called in context of > capture kernel, we can dynamically lower driver memory requirement (at > cost of lower IO throughout of-course, which is ok for this brief > context). > > You can parse the command line and look for presence of elfcorehdr= > option. > This is internally appended to command line by kexec tools to tell > capture > kernel the address of ELF core headers. > > > [AM] Is this a standard way? Doesn't look like one. According to > kernel-parameters.txt, kexec would "generally" pass this option to > kernel command line. Can we look at "struct resource crashk_res" and > check if start and end member have different value, which indicates > capture kernel? > Well, nobody else so far has had such requirements so can't say if this is standard way. But this is the best way I can think of so far. Using crashk_res will not work. Not all users will use kdump and will not reserve any memory for capture kernel. In that case crashk_res will be zero for start and end and you don't want to trim down the functionality of your driver. > What's the memory allocation requirement of current RAID driver? How > much > memory you are reserving for capture kernel? Are you already seeing the > memory allocation failure? > > [AM] Our normal runtime memory is about 20MB. For the test beds, we use > "crashkernel=192M at 16M". We have not yet seen the allocation failure but > we would like to build the fallback mechanism if it does fail under > capture kernel. Only if we are not able to get the normal runtime > memory, we plan to switch to a lower memory model. > 20MB is huge. I agree that it is a good idea to bring it down for capture kernel if performance is not significantly impacted. > I feel until and unless memory requirements are huge, we should not > compromise with IO throughput. Capability to save the dump to disk as > fast > as possible to reduce the down time is also an important consideration. > > [AM] We believe our normal runtime memory requirement is significant. > Also, even with the lower memory, there would not be a noticeable dump > time difference since lot of memory is for supporting multiple > outstanding commands in driver's raid core and other raid operations, > which will not be running under capture kernel. Thanks again for your > feedback. > Makes sense. Thanks Vivek
