About 'hash' event trigger patchset

About 'hash' event trigger patchset

[Namhyung Kim]

Hi Tom,

(Sorry for replying in another thread, I have a problem on mail settings)

I've just read your hash event trigger series, and want to give some feedback.

At first, the change log of 5/5 is actually a better documentation
than in patch 4/5 so I think it should be added to the doc also.  But
the syntax of the hash trigger should be look like:

- # echo hash:key(s):value(s)[:sort_keys()][ if filter] > event/trigger
+ # echo hash:key(s):value(s)[:"sort="sort_key(s)][ if filter] > event/trigger

Also on first example in the changelog of 5/5, key should be
'stacktrace' instead of 'call_site'.

As far as I see in the code, the sort key can receive an optional
descending/ascending modifier, but it's not documented.

One thing I noticed in the main logic is that it seems there's no
limit checking when adding/creating new entry.  In
hash_trigger_entry_create(), there's a check against max_entries but
if it goes beyond the max, it'd just access a NULL pointer AFAICS.  Am
I missing something?  Also I don't know what the difference between
->n_entries and ->total_entries (in hash_data).

I guess you wanted to set ->drops in that case, but I cannot find
where it gets set.  And I'm not sure it's good to check ->drop first,
since entry can find an existing entry and merged to it even if it
reached the max already.

Thanks,
Namhyung

Re: About 'hash' event trigger patchset

[Tom Zanussi]

Hi Namhyung,

On Wed, 2014-04-02 at 08:31 +0000, Namhyung Kim wrote:
> Hi Tom,
> 
> (Sorry for replying in another thread, I have a problem on mail settings)
> 
> I've just read your hash event trigger series, and want to give some feedback.
> 
> At first, the change log of 5/5 is actually a better documentation
> than in patch 4/5 so I think it should be added to the doc also.  But

Good point, I'll do that (after trimming it down a bit).

> the syntax of the hash trigger should be look like:
> 
> - # echo hash:key(s):value(s)[:sort_keys()][ if filter] > event/trigger
> + # echo hash:key(s):value(s)[:"sort="sort_key(s)][ if filter] > event/trigger
> 
> Also on first example in the changelog of 5/5, key should be
> 'stacktrace' instead of 'call_site'.
> 

Yeah, I realized that just after posting - will fix.

> As far as I see in the code, the sort key can receive an optional
> descending/ascending modifier, but it's not documented.
> 

I knew I was forgetting something ;-)  Thanks for pointing it out.

> One thing I noticed in the main logic is that it seems there's no
> limit checking when adding/creating new entry.  In
> hash_trigger_entry_create(), there's a check against max_entries but
> if it goes beyond the max, it'd just access a NULL pointer AFAICS.  Am
> I missing something?  Also I don't know what the difference between
> ->n_entries and ->total_entries (in hash_data).
> 
> I guess you wanted to set ->drops in that case, but I cannot find

Yes, the code is missing a very important snippet, which I realized
after hitting the problem.  My current code has this:

        if (hash_data->drops)
                return NULL;
        else if (hash_data->n_entries == hash_data->max_entries) {
                hash_data->drops = 1;
                return NULL;
        }

n_entries is the current number of entries used up, and max_entries is
the total number of available entries (a cached value to avoid
calculating it every time).

> where it gets set.  And I'm not sure it's good to check ->drop first,
> since entry can find an existing entry and merged to it even if it
> reached the max already.
> 

The assumption is that if you have any drops at all, you probably want
to redo the test with a bigger table, but regardless the data reflects
the situation up to the point the drops started happening.  Letting
events that already have a entry merge while rejecting those that don't
would invalidate the data you already have.

Thanks for taking a look and for your helpful comments,

Tom

> Thanks,
> Namhyung

Re: About 'hash' event trigger patchset

[Namhyung Kim]

Hi Tom,

On Wed, 02 Apr 2014 09:51:54 -0500, Tom Zanussi wrote:
> Hi Namhyung,
>
> On Wed, 2014-04-02 at 08:31 +0000, Namhyung Kim wrote:
>> One thing I noticed in the main logic is that it seems there's no
>> limit checking when adding/creating new entry.  In
>> hash_trigger_entry_create(), there's a check against max_entries but
>> if it goes beyond the max, it'd just access a NULL pointer AFAICS.  Am
>> I missing something?  Also I don't know what the difference between
>> ->n_entries and ->total_entries (in hash_data).
>> 
>> I guess you wanted to set ->drops in that case, but I cannot find
>
> Yes, the code is missing a very important snippet, which I realized
> after hitting the problem.  My current code has this:
>
>         if (hash_data->drops)
>                 return NULL;

I think this part can be omitted since it's already checked earlier.
But it's a minor issue.


>         else if (hash_data->n_entries == hash_data->max_entries) {
>                 hash_data->drops = 1;
>                 return NULL;
>         }
>
> n_entries is the current number of entries used up, and max_entries is
> the total number of available entries (a cached value to avoid
> calculating it every time).

But there's "total_entries" - increased in hash_trigger_entry_insert() -
too and I think it's just same as n_entries.

>
>> where it gets set.  And I'm not sure it's good to check ->drop first,
>> since entry can find an existing entry and merged to it even if it
>> reached the max already.
>> 
>
> The assumption is that if you have any drops at all, you probably want
> to redo the test with a bigger table, but regardless the data reflects
> the situation up to the point the drops started happening.  Letting
> events that already have a entry merge while rejecting those that don't
> would invalidate the data you already have.

Okay, I won't insist on it.

Thanks,
Namhyung

Re: About 'hash' event trigger patchset

[Tom Zanussi]

Hi Namhyung,

On Fri, 2014-04-04 at 16:36 +0900, Namhyung Kim wrote:
> Hi Tom,
> 
> On Wed, 02 Apr 2014 09:51:54 -0500, Tom Zanussi wrote:
> > Hi Namhyung,
> >
> > On Wed, 2014-04-02 at 08:31 +0000, Namhyung Kim wrote:
> >> One thing I noticed in the main logic is that it seems there's no
> >> limit checking when adding/creating new entry.  In
> >> hash_trigger_entry_create(), there's a check against max_entries but
> >> if it goes beyond the max, it'd just access a NULL pointer AFAICS.  Am
> >> I missing something?  Also I don't know what the difference between
> >> ->n_entries and ->total_entries (in hash_data).
> >> 
> >> I guess you wanted to set ->drops in that case, but I cannot find
> >
> > Yes, the code is missing a very important snippet, which I realized
> > after hitting the problem.  My current code has this:
> >
> >         if (hash_data->drops)
> >                 return NULL;
> 
> I think this part can be omitted since it's already checked earlier.
> But it's a minor issue.
> 

Right, exactly, it's completely redundant.

> 
> >         else if (hash_data->n_entries == hash_data->max_entries) {
> >                 hash_data->drops = 1;
> >                 return NULL;
> >         }
> >
> > n_entries is the current number of entries used up, and max_entries is
> > the total number of available entries (a cached value to avoid
> > calculating it every time).
> 
> But there's "total_entries" - increased in hash_trigger_entry_insert() -
> too and I think it's just same as n_entries.
> 

And this is too - in a previous version they could be different, but
you're right, n_entries is sufficient now - I'll consolidate in the next
version.

Thanks,

Tom

> >
> >> where it gets set.  And I'm not sure it's good to check ->drop first,
> >> since entry can find an existing entry and merged to it even if it
> >> reached the max already.
> >> 
> >
> > The assumption is that if you have any drops at all, you probably want
> > to redo the test with a bigger table, but regardless the data reflects
> > the situation up to the point the drops started happening.  Letting
> > events that already have a entry merge while rejecting those that don't
> > would invalidate the data you already have.
> 
> Okay, I won't insist on it.
> 
> Thanks,
> Namhyung