lkml.org 
[lkml]   [2011]   [Jul]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] dma-debug: hash_bucket_find needs to allow for offsets within an entry
    On Wed, Jul 20, 2011 at 12:38:13PM +0200, Roedel, Joerg wrote:
    > Hi Neil,
    >
    > thanks for your work on this :)
    >
    > On Tue, Jul 19, 2011 at 01:41:18PM -0400, Neil Horman wrote:
    > > lib/dma-debug.c | 17 +++++++++++++++--
    > > 1 files changed, 15 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/lib/dma-debug.c b/lib/dma-debug.c
    > > index db07bfd..333f0ee 100644
    > > --- a/lib/dma-debug.c
    > > +++ b/lib/dma-debug.c
    > > @@ -248,10 +248,23 @@ static struct dma_debug_entry *hash_bucket_find(struct hash_bucket *bucket,
    > > {
    > > struct dma_debug_entry *entry, *ret = NULL;
    > > int matches = 0, match_lvl, last_lvl = 0;
    > > + u64 estart, eend, rstart, rend;
    > > +
    > > + rstart = ref->dev_addr;
    > > + rend = rstart + ref->size;
    > >
    > > list_for_each_entry(entry, &bucket->list, list) {
    > > - if ((entry->dev_addr != ref->dev_addr) ||
    > > - (entry->dev != ref->dev))
    > > + estart = entry->dev_addr;
    > > + eend = estart + entry->size;
    > > +
    > > + /*
    > > + * An entry matches if the address range specified by the ref
    > > + * dev_addr and size falls entirely within the range specified
    > > + * by the entries dev_addr and size and the devices match
    > > + */
    > > + if (entry->dev != ref->dev)
    > > + continue;
    > > + if ((estart > rstart) || (eend < rend))
    > > continue;
    > >
    > > /*
    >
    > 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.

    > 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
    Neil

    >
    > Thanks,
    >
    > Joerg
    >
    > --
    > AMD Operating System Research Center
    >
    > Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach
    > General Managers: Alberto Bozzo, Andrew Bowd
    > Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632
    >
    >


    \
     
     \ /
      Last update: 2011-07-20 13:15    [W:5.865 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site