Messages in this thread | | | Date | Wed, 20 Jul 2011 15:29:25 +0200 | From | "Roedel, Joerg" <> | Subject | Re: [PATCH] dma-debug: hash_bucket_find needs to allow for offsets within an entry |
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On Wed, Jul 20, 2011 at 07:11:56AM -0400, Neil Horman wrote: > On Wed, Jul 20, 2011 at 12:38:13PM +0200, Roedel, Joerg wrote:
> > But it is not that easy. The hash_fn works on the dev_addr, this means > > to search all entries which might match you need to scan multiple > > hash-buckets potentially. > > In fact, you need to scan > > > > hash_fn(estart) <= idx <= hash_fn(eend) > > > Ah, good point. Its actually a bit more difficult that what you describe I > think. Given a ref->dev_addr, this check needs to find the entry in any bucket > for a matching device that has an entry->dev_addr less than ref->dev_addr, where > the former has a larger size than the latter. And since we don't know the true > size of the entry we are looking for, we could have crossed the HASH_FN_SHIFT > many times over to get to the ref->dev addr that was passed in. It almost > sounds like the hash table for this needs to be accessible by device rather than > by address.
You are right. We need to scan
0 <= idx <= hash_fn(rstart)
Probably we can fix that with a better hash-function. Any ideas? Using the device is not an option because then all entries would end up in only a few buckets. This will impact scanning performance too much.
For now, the partial syncs seem to happen rarely enough so that we can make it a slow-path. It is probably the best to do the exact scan first and do the full scan only if exact-scan failed (until we come up with a better solution).
> > to be sure. The patch above also lifts up the check_unmap which is not > > desired. > Hm, you're right, I suppose we need to add an exact map option to the passed in > ref structure or some such, I'll rework this
Thanks,
Joerg
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