On Wed 15 Aug 2012 08:29:38 PM MST, Jack Wang wrote: > 2012/8/16 Dave Jiang <dave.jiang@xxxxxxxxx>: >> On 08/15/2012 04:51 AM, John McCabe-Dansted wrote: >>> On Wed, Aug 15, 2012 at 7:30 PM, C Sights <csights@xxxxxxxxxxx> wrote: >>>> Hi all, >>>> Has anyone tried creating a bcache device in RAM and benchmarking >>>> performance of that versus just allowing that RAM to be used as file system >>>> buffers? >>> I doubt it; bcache is designed to use non-volatile flash memory rather >>> than ram. >>> >>> If the filesystem is readonly, I imagine that using RAM for bcache >>> would lead to worse performance as it would just add overhead. If the >>> filesystem is read-write then it might lead to better performance but >>> would also lead to the file-system being trashed on if unexpected >>> power loss occurs. >>> >>> Under what circumstance would you intend to actually use ram backed bcache? >>> >> >> So the Intel Xeon E5-2600 series platforms has this feature called >> asynchronous DRAM refresh (ADR). Essentially it's battery backed DRAM on >> per DIMM socket basis. I have written a RAM disk driver on top of that >> experimentally and played a little bit with it used by bcache instead of >> SSD. Writing to the memory region isn't going to be as fast as normal >> cached RAM because you have to ensure the data is flushed to the DRAM. >> However, read should be the same as cached DRAM. But the writing should >> still be faster than SSD. Anyhow, I'm more curious as to how I can >> benchmark this to demonstrate if this is a benefit with bcache. i.e. >> what benchmarking tool(s) I should use and with what parameters etc. >> > Hi Dave, > > Intesting, wish to see the result. what cache mode is intended to use with ADR. > > Jack > -- Jack, Right now I'm using wb mode for cache. However when I write I call clflush_cache_range() and then read the last dword to make really sure that everything has made it to the DRAM. I do wish it's possible on IA to just flush without invalidate the cache though. -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
