Re: [PATCH v2] opensm: Multicast root switch calculation

[Sasha Khapyorsky <sashak-smomgflXvOZWk0Htik3J/w@public.gmane.org>]

On 13:32 Wed 20 Jan     , Slava Strebkov wrote:
> "average hops" was chosen instead of "max hops" because in root weight
> calculation the number of ports is also important, not only the distance
> (hops).

But this patch is declared as root switch calculation optimization, not
as algorithm change (actually I even missed this part in V1).

If you think that an algorithm should be changed we need to handle this
separately.

And there could be a discussion - I have report that some days ago
credit loop issue was observed when "average hops" method was used
(and then it was replaced by "max hops"). I don't have much details
about this case and cannot be sure that it was not "false alarm" (or
outdated information), but anyway I think that we should be careful
here.

Sasha



> -----Original Message-----
> From: Sasha Khapyorsky [mailto:sashakvolt-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org] On Behalf Of Sasha
> Khapyorsky
> Sent: Wednesday, January 20, 2010 12:27 PM
> To: Slava Strebkov
> Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Eli Dorfman; Or Gerlitz; Yevgeny
> Kliteynik
> Subject: Re: [PATCH v2] opensm: Multicast root switch calculation
> 
> Hi Slava,
> 
> On 16:11 Thu 03 Dec     , Slava Strebkov wrote:
> > Proposed new algorithm for calculation of root switch for multicast
> > spanning tree. Only edge switches(those connected to hosts) and
> > switches - multicast members themselves are involved in root
> calculation.
> > This gives improvement, especially on large fabrics, since number of
> > switches usually much less then the number of ports, shared same mcast
> > group.
> > 
> > Signed-off-by: Slava Strebkov <slavas-smomgflXvOZWk0Htik3J/w@public.gmane.org>
> > ---
> 
> [snip]
> 
> > @@ -231,32 +342,27 @@ static float
> osm_mcast_mgr_compute_max_hops(osm_sm_t * sm, cl_qlist_t * l,
> >     of the multicast group.
> >
> **********************************************************************/
> >  static osm_switch_t *mcast_mgr_find_optimal_switch(osm_sm_t * sm,
> > -						   cl_qlist_t *list)
> > +						   cl_qlist_t * list)
> >  {
> >  	cl_qmap_t *p_sw_tbl;
> >  	osm_switch_t *p_sw, *p_best_sw = NULL;
> >  	float hops = 0;
> >  	float best_hops = 10000;	/* any big # will do */
> > -#ifdef OSM_VENDOR_INTF_ANAFA
> > -	boolean_t use_avg_hops = TRUE;	/* anafa2 - bug hca on switch
> *//* use max hops for root */
> > -#else
> > -	boolean_t use_avg_hops = FALSE;	/* use max hops for root */
> > -#endif
> > -
> > +	cl_qmap_t mcast_member_sw_tbl;
> >  	OSM_LOG_ENTER(sm->p_log);
> >  
> >  	p_sw_tbl = &sm->p_subn->sw_guid_tbl;
> >  
> > +	mcast_mgr_build_switch_map(sm, list, &mcast_member_sw_tbl);
> >  	for (p_sw = (osm_switch_t *) cl_qmap_head(p_sw_tbl);
> >  	     p_sw != (osm_switch_t *) cl_qmap_end(p_sw_tbl);
> >  	     p_sw = (osm_switch_t *) cl_qmap_next(&p_sw->map_item)) {
> >  		if (!osm_switch_supports_mcast(p_sw))
> >  			continue;
> >  
> > -		if (use_avg_hops)
> > -			hops = osm_mcast_mgr_compute_avg_hops(sm, list,
> p_sw);
> > -		else
> > -			hops = osm_mcast_mgr_compute_max_hops(sm, list,
> p_sw);
> > +		hops =
> > +		    osm_mcast_mgr_compute_avg_hops_weight(sm, p_sw,
> > +
> &mcast_member_sw_tbl);
> 
> Any reason why was root switch computation method changed? By default it
> was "max hops" based and as far as I can see you changed this to
> "average hops".
> 
> Sasha
> 
> >  
> >  		OSM_LOG(sm->p_log, OSM_LOG_DEBUG,
> >  			"Switch 0x%016" PRIx64 ", hops = %f\n",
> > @@ -277,6 +383,7 @@ static osm_switch_t
> *mcast_mgr_find_optimal_switch(osm_sm_t * sm,
> >  		OSM_LOG(sm->p_log, OSM_LOG_VERBOSE,
> >  			"No multicast capable switches detected\n");
> >  
> > +	mcast_mgr_destroy_switch_map(sm, &mcast_member_sw_tbl);
> >  	OSM_LOG_EXIT(sm->p_log);
> >  	return p_best_sw;
> >  }
> > -- 
> > 1.6.3.3
> > 
> > --
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> 
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