[PATCH] mlx4: allow for 4K mtu configuration of IB ports

[PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Or Gerlitz]

Since there's a dependency between the port mtu to the maximal
number of VLs the port can support - act in a loop, going down
from the highest possible number of VLs to the lowest. Use the
firmware return status as an indication for the requested number
of VLs being impossible with that mtu.

Signed-off-by: Or Gerlitz <ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>

---

Roland, this is an updated approach and posting for the patch posted
earlier by Vlad on which you've responded @
http://www.spinics.net/lists/linux-rdma/msg02136.html
I've attempted to address your comment and questions, let me know...

 drivers/net/mlx4/port.c |   36 ++++++++++++++++++++++++++++++++----
 1 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/drivers/net/mlx4/port.c b/drivers/net/mlx4/port.c
index 8856659..872e8d3 100644
--- a/drivers/net/mlx4/port.c
+++ b/drivers/net/mlx4/port.c
@@ -43,6 +43,10 @@
 #define MLX4_VLAN_VALID		(1u << 31)
 #define MLX4_VLAN_MASK		0xfff

+static int mlx4_ib_set_4k_mtu;
+module_param_named(set_4k_mtu, mlx4_ib_set_4k_mtu, int, 0444);
+MODULE_PARM_DESC(set_4k_mtu, "attempt to set 4K MTU to IB ports");
+
 void mlx4_init_mac_table(struct mlx4_dev *dev, struct mlx4_mac_table *table)
 {
 	int i;
@@ -461,10 +465,20 @@ int mlx4_get_port_ib_caps(struct mlx4_dev *dev, u8 port, __be32 *caps)
 	return err;
 }

+/* bit locations for set port command with zero op modifier */
+enum {
+	MLX4_SET_PORT_VL_CAP	 = 4, /* bits 7:4 */
+	MLX4_SET_PORT_MTU_CAP	 = 12, /* bits 15:12 */
+	MLX4_CHANGE_PORT_VL_CAP	 = 21,
+	MLX4_CHANGE_PORT_MTU_CAP = 22,
+};
+
+#define IBTA_MTU_4096	5
+
 int mlx4_SET_PORT(struct mlx4_dev *dev, u8 port)
 {
 	struct mlx4_cmd_mailbox *mailbox;
-	int err;
+	int err, vl_cap;

 	if (dev->caps.port_type[port] == MLX4_PORT_TYPE_ETH)
 		return 0;
@@ -474,10 +488,24 @@ int mlx4_SET_PORT(struct mlx4_dev *dev, u8 port)
 		return PTR_ERR(mailbox);

 	memset(mailbox->buf, 0, 256);
-
 	((__be32 *) mailbox->buf)[1] = dev->caps.ib_port_def_cap[port];
-	err = mlx4_cmd(dev, mailbox->dma, port, 0, MLX4_CMD_SET_PORT,
-		       MLX4_CMD_TIME_CLASS_B);
+
+	if (mlx4_ib_set_4k_mtu)
+		for (vl_cap = 8; vl_cap >= 1; vl_cap >>= 1) {
+			((__be32 *) mailbox->buf)[0] = cpu_to_be32(
+				(1 << MLX4_CHANGE_PORT_MTU_CAP) |
+				(1 << MLX4_CHANGE_PORT_VL_CAP)	|
+				(IBTA_MTU_4096 << MLX4_SET_PORT_MTU_CAP) |
+				(vl_cap << MLX4_SET_PORT_VL_CAP));
+			err = mlx4_cmd(dev, mailbox->dma, port, 0,
+				MLX4_CMD_SET_PORT, MLX4_CMD_TIME_CLASS_B);
+			if (err != -ENOMEM)
+				break;
+		}
+	else {
+		err = mlx4_cmd(dev, mailbox->dma, port, 0, MLX4_CMD_SET_PORT,
+			       MLX4_CMD_TIME_CLASS_B);
+	}

 	mlx4_free_cmd_mailbox(dev, mailbox);
 	return err;
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Roland Dreier]

On Wed, May 25, 2011 at 5:10 AM, Or Gerlitz <ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> wrote:
> Roland, this is an updated approach and posting for the patch posted
> earlier by Vlad on which you've responded @
> http://www.spinics.net/lists/linux-rdma/msg02136.html
> I've attempted to address your comment and questions, let me know...

Thanks for looking at this again.  Definitely better in terms of
fewer magic numbers... however I still think needing to set this
with a module parameter kind of sucks for the end user.  Can
we think of a better way to handle this?

Is the issue that we trade off VL cap for MTU?
Does anyone really care about max VL cap with 2K MTU?

 - R.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Or Gerlitz]

Roland Dreier <roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:

> Is the issue that we trade off VL cap for MTU?

yes, this is it

> [...] however I still think needing to set this with a module parameter kind of
> sucks for the end user.  Can we think of a better way to handle this?

with the above @ hand, setting mtu cap of 4k w.o an ability of
reducing that to 2k, makes the patch distruptive for users that do
need eight VLs. Maybe it would be easier for the common user if turn
on the module param by default.

> Does anyone really care about max VL cap with 2K MTU?

I'm not with you... can you elaborate a little further here? the
current HW generation support four VLs with 4k mtu, newer HW might
support more.

Or.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Roland Dreier]

On Wed, May 25, 2011 at 2:05 PM, Or Gerlitz <or.gerlitz-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> Does anyone really care about max VL cap with 2K MTU?
>
> I'm not with you... can you elaborate a little further here? the
> current HW generation support four VLs with 4k mtu, newer HW might
> support more.

I mean is there anyone who really uses >4 VLs?  Presumably the
HW designers didn't think so, because they limited HW to 4 VLs
with 4K MTU.

At least can we make this a runtime thing?  If we're able to set a
port as IB vs ethernet then # of VLs seems like it should be doable too.

And 4K MTU should probably be the default, since almost all users
want 4K MTU vs. caring about VLs.  (Probably 99% of IB users
never set SL of anything)

 - R.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Or Gerlitz]

Roland Dreier <roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:

> And 4K MTU should probably be the default, since almost all users
> want 4K MTU vs. caring about VLs.  (Probably 99% of IB users
> never set SL of anything)

I agree that we want that to be the default, I'm not sure the 99%
thing is accurate, with more and more (specifically the huge ones) IB
clusters that are built in some sort of 2D/3D torus, mesh or alike
topologies for which routing engines such as DOR and LASH use multiple
VLs to avoid credit loops. also I assume that some users (maybe < 5%)
would like to enjoy 8 HW traffic classes, so if pressed to the wall,
they would prefer 2k mtu with the current HW.

> I mean is there anyone who really uses >4 VLs?  Presumably the
> HW designers didn't think so, because they limited HW to 4 VLs with 4K MTU.

I'm not sure if 4 VLs are enough for all the topologies / algorithms I
mentioned above, so I do prefer to leave an option to run with eight
VLs. As for the HW designers comment, its always good to look forward
for improvements in newer HCA drops (the patch for the CX3 series
device IDs is already comitted by
31dd272e8cbb32ef31a411492cc642c363bb54b9, so one can expect for the
actual cards to be coming soon as well).

> At least can we make this a runtime thing?  If we're able to set a
> port as IB vs ethernet then # of VLs seems like it should be doable too.

Here I lost you again, the policy is dictated by the module param,
which whose default value should be turned on, the code that sets the
mtu and VL cap is executed each time the function change by the patch
is called, which in turn happens each time an IB link type is sensed
or dictated for the port.

Or.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Jason Gunthorpe]

On Thu, May 26, 2011 at 12:46:20AM +0300, Or Gerlitz wrote:

> > I mean is there anyone who really uses >4 VLs? ?Presumably the
> > HW designers didn't think so, because they limited HW to 4 VLs with 4K MTU.
> 
> I'm not sure if 4 VLs are enough for all the topologies / algorithms I
> mentioned above, so I do prefer to leave an option to run with eight
> VLs. As for the HW designers comment, its always good to look
> forward

Routing algorithms only need VLs on interswitch links, not on HCA to
switch links. The only use of the HCA to switch VLs is for QoS. Mesh
topologies can usually be routed with only two VLs, but you need alot
of SLs to make that work.

IMHO it would be much nicer if the SM could control and set this
choice, but since the spec doesn't have a provision for this I'm not
sure what to suggest there..

Jason
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Roland Dreier]

On Wed, May 25, 2011 at 2:46 PM, Or Gerlitz <or.gerlitz-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> At least can we make this a runtime thing?  If we're able to set a
>> port as IB vs ethernet then # of VLs seems like it should be doable too.
>
> Here I lost you again, the policy is dictated by the module param,
> which whose default value should be turned on, the code that sets the
> mtu and VL cap is executed each time the function change by the patch
> is called, which in turn happens each time an IB link type is sensed
> or dictated for the port.

I mean set the MTU port-by-port with the module loaded, the same way
we are supposed to be able to do for the port type.  Rather than having
one global module parameter.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Or Gerlitz]

Roland Dreier wrote:
> I mean set the MTU port-by-port with the module loaded, the same way
> we are supposed to be able to do for the port type.  Rather than having
> one global module parameter.

The HCA has set of per port buffers, from which comes the dependency 
between VLs to MTU. So with this code running for each IB hca/port, 
we're actually doing that logic port-by-port. I assume you didn't mean 
let the user specify a desired MTU for each hca/port... or I'm still not 
fully with you?

Anyway, I'd be happy to provide at least the folks that use torus/mesh 
and/or sophisticated QoS schemes an ability to use eight VLs with the 
current HW, so how about keeping the module param but with default value 
turned on?

Or.

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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Roland Dreier]

On Wed, May 25, 2011 at 11:24 PM, Or Gerlitz <ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> wrote:
> Roland Dreier wrote:
>>
>> I mean set the MTU port-by-port with the module loaded, the same way
>> we are supposed to be able to do for the port type.  Rather than having
>> one global module parameter.
>
> The HCA has set of per port buffers, from which comes the dependency between
> VLs to MTU. So with this code running for each IB hca/port, we're actually
> doing that logic port-by-port. I assume you didn't mean let the user specify
> a desired MTU for each hca/port... or I'm still not fully with you?
>
> Anyway, I'd be happy to provide at least the folks that use torus/mesh
> and/or sophisticated QoS schemes an ability to use eight VLs with the
> current HW, so how about keeping the module param but with default value
> turned on?

What I'm trying to say is that a global module parameter is a pain for users.
Would it make sense to have a "port_type" module parameter where you could
set all the ports to IB or to ethernet, and have no way to have a mix of port
types or change without reloading the module?

The obvious answer is no, and therefore we have mlx4_portX  attributes in
sysfs that are per port.  MTU is the same way.  For example, you suggest
that CX3 won't have the same limitation of only 4 VLs with 4K MTU.  In
that case, think about a system with one CX2 and one CX3 -- should the
CX3 be limited to 2K MTU because of CX2 limitations?

Rather than having a completely different way of handling MTU, why can't
we just handle it the same way as the port type, and have a sysfs attribute
like "mlx4_mtuN" for each port?

 - R.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Or Gerlitz]

 Roland Dreier <roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> The obvious answer is no, and therefore we have mlx4_portX  attributes in
> sysfs that are per port.  MTU is the same way.  For example, you suggest
> that CX3 won't have the same limitation of only 4 VLs with 4K MTU.  In
> that case, think about a system with one CX2 and one CX3 -- should the
> CX3 be limited to 2K MTU because of CX2 limitations?
>
> Rather than having a completely different way of handling MTU, why can't
> we just handle it the same way as the port type, and have a sysfs attribute
> like "mlx4_mtuN" for each port?

okay, got that. I'd like to make another round of thinking / checking if we
can make 4k mtu being the default and not configurable also for
pre-CX3 devices,
if yes, I guess we can avoid the per port sysfs entry, if not, I'll add that as
part of the patch.

Or.
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RE: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Bob Pearson]

With lash+mesh redsky required 6-7 VLs to wire up without deadlocks. I think
that Jim's version uses 8 SLs but only 2VLs to work.
If someone was using a torus and also wanted to support QOS and also wanted
to separate multicast and management on a separate VL to be absolutely sure
that there is no possibility of a deadlock you might end up with #QOS * 2 +
1 which would be 5 using the current algorithm.

-----Original Message-----
From: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
[mailto:linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org] On Behalf Of Roland Dreier
Sent: Wednesday, May 25, 2011 4:28 PM
To: Or Gerlitz
Cc: Or Gerlitz; linux-rdma; Vladimir Sokolovsky
Subject: Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

On Wed, May 25, 2011 at 2:05 PM, Or Gerlitz <or.gerlitz-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> Does anyone really care about max VL cap with 2K MTU?
>
> I'm not with you... can you elaborate a little further here? the 
> current HW generation support four VLs with 4k mtu, newer HW might 
> support more.

I mean is there anyone who really uses >4 VLs?  Presumably the HW designers
didn't think so, because they limited HW to 4 VLs with 4K MTU.

At least can we make this a runtime thing?  If we're able to set a port as
IB vs ethernet then # of VLs seems like it should be doable too.

And 4K MTU should probably be the default, since almost all users want 4K
MTU vs. caring about VLs.  (Probably 99% of IB users never set SL of
anything)

 - R.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Roland Dreier]

On Wed, May 25, 2011 at 3:19 PM, Bob Pearson
<rpearson-klaOcWyJdxkshyMvu7JE4pqQE7yCjDx5@public.gmane.org> wrote:
> With lash+mesh redsky required 6-7 VLs to wire up without deadlocks. I think
> that Jim's version uses 8 SLs but only 2VLs to work.
> If someone was using a torus and also wanted to support QOS and also wanted
> to separate multicast and management on a separate VL to be absolutely sure
> that there is no possibility of a deadlock you might end up with #QOS * 2 +
> 1 which would be 5 using the current algorithm.

But again you don't need all those VLs on the HCAs' links, do you?

 - R.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Or Gerlitz]

Roland Dreier wrote:
> Bob Pearson <rpearson-klaOcWyJdxkshyMvu7JE4pqQE7yCjDx5@public.gmane.org> wrote:
>> With lash+mesh redsky required 6-7 VLs to wire up without deadlocks. I think
>> that Jim's version uses 8 SLs but only 2VLs to work.
>> If someone was using a torus and also wanted to support QOS and also wanted
>> to separate multicast and management on a separate VL to be absolutely sure
>> that there is no possibility of a deadlock you might end up with #QOS * 2 +
>> 1 which would be 5 using the current algorithm.

> But again you don't need all those VLs on the HCAs' links, do you?

Jason Gunthorpe wrote:
> Routing algorithms only need VLs on interswitch links, not on HCA to
> switch links. The only use of the HCA to switch VLs is for QoS. Mesh
> topologies can usually be routed with only two VLs, but you need alot
> of SLs to make that work.

Bob, Jim, Alex

I wasn't sure if the SL-to-VL mapping done by open SM is dictated by the 
directives @ the user config file or if the routing algorithm is "VL 
aware" but the routing engine? if the latter, do interswitch links use 
different mapping vs. HCA - switch links?

Or.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Jim Schutt]

Or Gerlitz wrote:
> Roland Dreier wrote:
>> Bob Pearson <rpearson-klaOcWyJdxkshyMvu7JE4pqQE7yCjDx5@public.gmane.org> wrote:
>>> With lash+mesh redsky required 6-7 VLs to wire up without deadlocks. 
>>> I think
>>> that Jim's version uses 8 SLs but only 2VLs to work.
>>> If someone was using a torus and also wanted to support QOS and also 
>>> wanted
>>> to separate multicast and management on a separate VL to be 
>>> absolutely sure
>>> that there is no possibility of a deadlock you might end up with #QOS 
>>> * 2 +
>>> 1 which would be 5 using the current algorithm.
> 
>> But again you don't need all those VLs on the HCAs' links, do you?
> 
> Jason Gunthorpe wrote:
>> Routing algorithms only need VLs on interswitch links, not on HCA to
>> switch links. The only use of the HCA to switch VLs is for QoS. Mesh
>> topologies can usually be routed with only two VLs, but you need alot
>> of SLs to make that work.
> 
> Bob, Jim, Alex
> 
> I wasn't sure if the SL-to-VL mapping done by open SM is dictated by the 
> directives @ the user config file or if the routing algorithm is "VL 
> aware" but the routing engine? if the latter, do interswitch links use 
> different mapping vs. HCA - switch links?

FWIW, the torus-2QoS routing engine uses VL bit 0 for torus deadlock
avoidance, VL bit 1 to route around a missing switch without deadlocks,
and VL bit 2 to provide two QoS levels.  It needs the port dependence
of the SL2VL maps to do this in switches.

The interswitch and HCAs use the same mapping, but only VL bit 2
is needed on HCAs, to provide the QoS levels.

I chose that bit usage because it seemed the proper ordering of
capabilities if there are fewer than 8 data VLs available - basic
deadlock avoidance is most important; some QoS is nice to have but
not that useful if the fabric can deadlock.

Is that what you were asking, at least WRT. torus-2QoS?

-- Jim

> 
> Or.
> 
> 


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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Jim Schutt]

Jim Schutt wrote:
> Or Gerlitz wrote:
>> Roland Dreier wrote:
>>> Bob Pearson <rpearson-klaOcWyJdxkshyMvu7JE4pqQE7yCjDx5@public.gmane.org> wrote:
>>>> With lash+mesh redsky required 6-7 VLs to wire up without deadlocks. 
>>>> I think
>>>> that Jim's version uses 8 SLs but only 2VLs to work.
>>>> If someone was using a torus and also wanted to support QOS and also 
>>>> wanted
>>>> to separate multicast and management on a separate VL to be 
>>>> absolutely sure
>>>> that there is no possibility of a deadlock you might end up with 
>>>> #QOS * 2 +
>>>> 1 which would be 5 using the current algorithm.
>>
>>> But again you don't need all those VLs on the HCAs' links, do you?
>>
>> Jason Gunthorpe wrote:
>>> Routing algorithms only need VLs on interswitch links, not on HCA to
>>> switch links. The only use of the HCA to switch VLs is for QoS. Mesh
>>> topologies can usually be routed with only two VLs, but you need alot
>>> of SLs to make that work.
>>
>> Bob, Jim, Alex
>>
>> I wasn't sure if the SL-to-VL mapping done by open SM is dictated by 
>> the directives @ the user config file or if the routing algorithm is 
>> "VL aware" but the routing engine? if the latter, do interswitch links 
>> use different mapping vs. HCA - switch links?
> 
> FWIW, the torus-2QoS routing engine uses VL bit 0 for torus deadlock
> avoidance, VL bit 1 to route around a missing switch without deadlocks,
> and VL bit 2 to provide two QoS levels.  It needs the port dependence
> of the SL2VL maps to do this in switches.
> 
> The interswitch and HCAs use the same mapping, but only VL bit 2
> is needed on HCAs, to provide the QoS levels.

It occurred to me as soon I sent the above that there's no
good reason to insist that the VL usage is the same for both
interswitch links, and switch-CA links.

Do I need to change this?

-- Jim

> 
> I chose that bit usage because it seemed the proper ordering of
> capabilities if there are fewer than 8 data VLs available - basic
> deadlock avoidance is most important; some QoS is nice to have but
> not that useful if the fabric can deadlock.
> 
> Is that what you were asking, at least WRT. torus-2QoS?
> 
> -- Jim
> 
>>
>> Or.
>>
>>
> 
> 
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> 
> 


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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Roland Dreier]

On Thu, May 26, 2011 at 7:30 AM, Jim Schutt <jaschut-4OHPYypu0djtX7QSmKvirg@public.gmane.org> wrote:
> It occurred to me as soon I sent the above that there's no
> good reason to insist that the VL usage is the same for both
> interswitch links, and switch-CA links.
>
> Do I need to change this?

I don't think changing this is a high priority, since it's a pretty small
slice of the world, and QoS on the edge links probably is important
to an even smaller slice, but IMHO it would be better to give QoS to
HCAs that only support 4 VLs by using a different SL2VL table for
links to CAs.

 - R.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Or Gerlitz]

Roland Dreier <roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
Jim Schutt <jaschut-4OHPYypu0djtX7QSmKvirg@public.gmane.org> wrote:
>> no good reason to insist that the VL usage is the same for both
>> interswitch links, and switch-CA links. Do I need to change this?

> I don't think changing this is a high priority, since it's a pretty small
> slice of the world, and QoS on the edge links probably is important
> to an even smaller slice, but IMHO it would be better to give QoS to
> HCAs that only support 4 VLs by using a different SL2VL table for links to CAs.

Jim,

AFAIK, the way opensm applies an SL-to-VL mapping specification (e.g
dictated by the admin or maybe your routing engine) on a specific link
is by modulation on the number of active VLs for that link - e.g say
the ID mapping was required and there are two VLs for that link, so
we'll have SL-to-VL of 0->0 1->1 2->0 3->1 and so on. So in that
respect, I wasn't sure what's the change here for you.

Or.
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Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

[Jim Schutt]

Hi Or,

Or Gerlitz wrote:
> Roland Dreier <roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> Jim Schutt <jaschut-4OHPYypu0djtX7QSmKvirg@public.gmane.org> wrote:
>>> no good reason to insist that the VL usage is the same for both
>>> interswitch links, and switch-CA links. Do I need to change this?
> 
>> I don't think changing this is a high priority, since it's a pretty small
>> slice of the world, and QoS on the edge links probably is important
>> to an even smaller slice, but IMHO it would be better to give QoS to
>> HCAs that only support 4 VLs by using a different SL2VL table for links to CAs.
> 
> Jim,
> 
> AFAIK, the way opensm applies an SL-to-VL mapping specification (e.g
> dictated by the admin or maybe your routing engine) on a specific link
> is by modulation on the number of active VLs for that link - e.g say
> the ID mapping was required and there are two VLs for that link, so
> we'll have SL-to-VL of 0->0 1->1 2->0 3->1 and so on. So in that
> respect, I wasn't sure what's the change here for you.

Hmmm, can you tell me where such remapping happens?

What I know about so far is the code in sl2vl_update_table(),
which AFAICS truncates VL values in the SL2VL maps provided
by the routing engine to fit into the number of VLs supported
by a port.

Am I missing something else?

torus-2QoS will currently only use VL values 0 and 4 in the
SL2VL maps it generates for CA ports; i.e. any SL maps either
to VL 0 or VL 4, depending on QoS level.

So sl2vl_update_table() would truncate all those VL 4 values
to 0 in the case of ports that support fewer than 8 data VLs.

What I'm suggesting is that I need to make torus-2QoS generate
SL2VL maps that only reference VLs 0 or 1 for CA ports, in order
to allow it to support 2 QoS levels for CA ports that don't
support 8 data VLs.

-- Jim

> 
> Or.
> 
> 


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