From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: <linux-cxl@vger.kernel.org>, <nvdimm@lists.linux.dev>,
<linux-pci@vger.kernel.org>, <patches@lists.linux.dev>,
<hch@lst.de>, "Ben Widawsky" <bwidawsk@kernel.org>
Subject: Re: [PATCH 36/46] cxl/region: Add interleave ways attribute
Date: Tue, 19 Jul 2022 15:47:18 +0100 [thread overview]
Message-ID: <20220719154718.000077ec@Huawei.com> (raw)
In-Reply-To: <62cb6f9a74b33_3535162944e@dwillia2-xfh.notmuch>
On Sun, 10 Jul 2022 17:32:26 -0700
Dan Williams <dan.j.williams@intel.com> wrote:
> Jonathan Cameron wrote:
> > On Thu, 23 Jun 2022 21:19:40 -0700
> > Dan Williams <dan.j.williams@intel.com> wrote:
> >
> > > From: Ben Widawsky <bwidawsk@kernel.org>
> > >
> > > Add an ABI to allow the number of devices that comprise a region to be
> > > set.
> >
> > Should at least mention interleave_granularity is being added as well!
>
> Added.
>
> >
> > >
> > > Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
> > > [djbw: reword changelog]
> > > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> >
> > Random diversion inline...
> >
> > > ---
> > > Documentation/ABI/testing/sysfs-bus-cxl | 21 ++++
> > > drivers/cxl/core/region.c | 128 ++++++++++++++++++++++++
> > > drivers/cxl/cxl.h | 33 ++++++
> > > 3 files changed, 182 insertions(+)
> >
> > > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> > > index f75978f846b9..78af42454760 100644
> > > --- a/drivers/cxl/core/region.c
> > > +++ b/drivers/cxl/core/region.c
> > > @@ -7,6 +7,7 @@
> >
> >
> > > +static ssize_t interleave_granularity_store(struct device *dev,
> > > + struct device_attribute *attr,
> > > + const char *buf, size_t len)
> > > +{
> > > + struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev->parent);
> > > + struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
> > > + struct cxl_region *cxlr = to_cxl_region(dev);
> > > + struct cxl_region_params *p = &cxlr->params;
> > > + int rc, val;
> > > + u16 ig;
> > > +
> > > + rc = kstrtoint(buf, 0, &val);
> > > + if (rc)
> > > + return rc;
> > > +
> > > + rc = granularity_to_cxl(val, &ig);
> > > + if (rc)
> > > + return rc;
> > > +
> > > + /* region granularity must be >= root granularity */
> >
> > In general I think that's an implementation choice. Sure today
> > we only support it this way, but it's perfectly possible to build
> > setups where that's not the case.
>
> If the region granularity is smaller than the host bridge interleave
> granularity it means that multiple devices per host bridge are needed to
> satsify a single "slot" in the interleave. Valid? Yes. Useful for Linux
> to support, not clear.
True. Wait and see on this one makes sense to me. I only noticed because
my older test scripts (against hacks on top of Ben's code) were broken as
I did it the silly way :)
>
> > Maybe the comment should say that this code goes with an
> > implementation choice inline with the software guide (that argues you
> > will always prefer small ig for interleaving at the host to make best
> > use of bandwidth etc).
>
> No, I would prefer that as far as the Linux implementation is concerned
> the software-guide does not exist. In the sense that the Linux
> implementation choices supersede and are otherwise a superset of what
> the guide recommends.
ah. I phrased that badly. I just meant lift the argument as a comment rather
than a cross reference.
>
> Also, for the same reason that the code does not anticipate future
> implementation possibilities, neither should the comments. It is
> sufficient to just change this comment when / if the implemetation stops
> expecting region granularity >= root granularity.
>
> > Interestingly the code I was previously testing QEMU with
> > allowed that option (might have been only option that worked).
> > That code was a mixture of Ben's earlier version and my own hacks.
> > It probably doesn't make sense to support other ways of picking
> > the interleaving granularity until / if we ever get a request
> > to do so.
> >
> > I think it results in a different device ordering.
> >
> > Ordering with this
> >
> > Host
> > | 4k
> > / \
> > / \
> > HB HB 8k
> > | |
> > / \ / \
> > 0 2 1 3
> >
> > Ordering with Larger granularity CFMWS over finer granularity HB
> >
> > Host
> > | 8k
> > / \
> > / \
> > HB HB 4k
> > | |
> > / \ / \
> > 0 1 2 3
> >
> > Not clear why you'd do the second one though :) So can ignore for now.
>
> All I can think of is "ZOMG! My platform failed and the only one I have
> to recover my data has HB interleaves with larger granularity than my
> failed system!". Otherwise, I expect cross-platform CXL persistent
> memory recovery to be so rare as to not need to spend time too much time
> worrying about it now. It seems a straightforward constraint to lift at
> a later date without any risk to breaking the ABI.
It was cross platform that I was thinking but you make a fair point that
it is unlikely to occur that often. + If another OS want's to do it wrong
that's their problem :)
J
next prev parent reply other threads:[~2022-07-19 14:47 UTC|newest]
Thread overview: 157+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-24 2:45 [PATCH 00/46] CXL PMEM Region Provisioning Dan Williams
2022-06-24 2:45 ` [PATCH 01/46] tools/testing/cxl: Fix cxl_hdm_decode_init() calling convention Dan Williams
2022-06-28 10:37 ` Jonathan Cameron
[not found] ` <CGME20220629174147uscas1p211384ae262e099484440ef285be26c75@uscas1p2.samsung.com>
2022-06-29 17:41 ` Adam Manzanares
2022-07-09 20:06 ` Dan Williams
2022-07-12 22:11 ` Adam Manzanares
2022-06-24 2:45 ` [PATCH 02/46] cxl/port: Keep port->uport valid for the entire life of a port Dan Williams
2022-06-24 3:37 ` Alison Schofield
2022-06-28 11:47 ` Jonathan Cameron
2022-06-28 14:27 ` Dan Williams
[not found] ` <CGME20220629174622uscas1p2236a084ce25771a3ab57c6f006632f35@uscas1p2.samsung.com>
2022-06-29 17:46 ` Adam Manzanares
2022-06-24 2:45 ` [PATCH 03/46] cxl/hdm: Use local hdm variable Dan Williams
2022-06-24 3:38 ` Alison Schofield
2022-06-28 15:16 ` Jonathan Cameron
[not found] ` <CGME20220629200312uscas1p292303b9325dcbfe59293f002dc9e6b03@uscas1p2.samsung.com>
2022-06-29 20:03 ` Adam Manzanares
2022-06-24 2:45 ` [PATCH 04/46] cxl/core: Rename ->decoder_range ->hpa_range Dan Williams
2022-06-24 3:39 ` Alison Schofield
2022-06-28 15:17 ` Jonathan Cameron
[not found] ` <CGME20220629200652uscas1p2c1da644ea63a5de69e14e046379779b1@uscas1p2.samsung.com>
2022-06-29 20:06 ` Adam Manzanares
2022-06-24 2:45 ` [PATCH 05/46] cxl/core: Drop ->platform_res attribute for root decoders Dan Williams
2022-06-28 15:24 ` Jonathan Cameron
2022-07-09 23:33 ` Dan Williams
[not found] ` <CGME20220629202117uscas1p2892fb68ae60c4754e2f7d26882a92ae5@uscas1p2.samsung.com>
2022-06-29 20:21 ` Adam Manzanares
2022-07-09 23:38 ` Dan Williams
2022-06-24 2:45 ` [PATCH 06/46] cxl/core: Drop is_cxl_decoder() Dan Williams
2022-06-24 3:48 ` Alison Schofield
2022-06-28 15:25 ` Jonathan Cameron
[not found] ` <CGME20220629203448uscas1p264a7f79a1ed7f9257eefcb3064c7d943@uscas1p2.samsung.com>
2022-06-29 20:34 ` Adam Manzanares
2022-06-24 2:45 ` [PATCH 07/46] cxl: Introduce cxl_to_{ways,granularity} Dan Williams
2022-06-28 15:36 ` Jonathan Cameron
2022-07-09 23:52 ` Dan Williams
2022-06-24 2:45 ` [PATCH 08/46] cxl/core: Define a 'struct cxl_switch_decoder' Dan Williams
2022-06-28 16:12 ` Jonathan Cameron
2022-06-30 10:56 ` Jonathan Cameron
2022-07-10 0:49 ` Dan Williams
2022-07-10 0:33 ` Dan Williams
2022-06-24 2:46 ` [PATCH 09/46] cxl/acpi: Track CXL resources in iomem_resource Dan Williams
2022-06-28 16:43 ` Jonathan Cameron
2022-07-10 2:12 ` Dan Williams
2022-07-19 14:24 ` Jonathan Cameron
2022-06-24 2:46 ` [PATCH 10/46] cxl/core: Define a 'struct cxl_root_decoder' for tracking CXL window resources Dan Williams
2022-06-28 16:49 ` Jonathan Cameron
2022-07-10 2:20 ` Dan Williams
2022-06-28 16:53 ` Jonathan Cameron
2022-06-24 2:46 ` [PATCH 11/46] cxl/core: Define a 'struct cxl_endpoint_decoder' for tracking DPA resources Dan Williams
2022-06-28 16:55 ` Jonathan Cameron
2022-07-10 2:40 ` Dan Williams
2022-06-24 2:46 ` [PATCH 12/46] cxl/mem: Convert partition-info to resources Dan Williams
2022-06-28 17:02 ` Jonathan Cameron
2022-06-24 2:46 ` [PATCH 13/46] cxl/hdm: Require all decoders to be enumerated Dan Williams
2022-06-28 17:04 ` Jonathan Cameron
2022-06-24 2:46 ` [PATCH 14/46] cxl/hdm: Enumerate allocated DPA Dan Williams
2022-06-29 14:43 ` Jonathan Cameron
2022-07-10 3:03 ` Dan Williams
2022-07-19 14:25 ` Jonathan Cameron
2022-06-24 2:46 ` [PATCH 15/46] cxl/Documentation: List attribute permissions Dan Williams
2022-06-28 3:16 ` Alison Schofield
2022-06-29 14:59 ` Jonathan Cameron
2022-06-24 2:46 ` [PATCH 16/46] cxl/hdm: Add 'mode' attribute to decoder objects Dan Williams
2022-06-29 15:28 ` Jonathan Cameron
2022-07-10 3:45 ` Dan Williams
2022-06-24 2:47 ` [PATCH 17/46] cxl/hdm: Track next decoder to allocate Dan Williams
2022-06-29 15:31 ` Jonathan Cameron
2022-07-10 3:55 ` Dan Williams
2022-07-19 14:27 ` Jonathan Cameron
2022-07-10 16:34 ` Dan Williams
2022-06-24 2:47 ` [PATCH 18/46] cxl/hdm: Add support for allocating DPA to an endpoint decoder Dan Williams
2022-06-29 15:56 ` Jonathan Cameron
2022-07-10 16:53 ` Dan Williams
2022-06-24 2:47 ` [PATCH 19/46] cxl/debug: Move debugfs init to cxl_core_init() Dan Williams
2022-06-29 15:58 ` Jonathan Cameron
2022-06-24 2:47 ` [PATCH 20/46] cxl/mem: Add a debugfs version of 'iomem' for DPA, 'dpamem' Dan Williams
2022-06-29 16:08 ` Jonathan Cameron
2022-07-10 17:09 ` Dan Williams
2022-06-24 2:47 ` [PATCH 21/46] tools/testing/cxl: Move cxl_test resources to the top of memory Dan Williams
2022-06-29 16:11 ` Jonathan Cameron
2022-07-10 17:19 ` Dan Williams
2022-06-24 2:47 ` [PATCH 22/46] tools/testing/cxl: Expand CFMWS windows Dan Williams
2022-06-29 16:14 ` Jonathan Cameron
2022-06-24 2:47 ` [PATCH 23/46] tools/testing/cxl: Add partition support Dan Williams
2022-06-29 16:20 ` Jonathan Cameron
2022-06-24 2:48 ` [PATCH 24/46] tools/testing/cxl: Fix decoder default state Dan Williams
2022-06-29 16:22 ` Jonathan Cameron
2022-07-10 17:33 ` Dan Williams
2022-06-24 2:48 ` [PATCH 25/46] cxl/port: Record dport in endpoint references Dan Williams
2022-06-29 16:49 ` Jonathan Cameron
2022-07-10 18:40 ` Dan Williams
2022-06-24 4:19 ` [PATCH 26/46] cxl/port: Record parent dport when adding ports Dan Williams
2022-06-29 17:02 ` Jonathan Cameron
2022-06-24 4:19 ` [PATCH 27/46] cxl/port: Move 'cxl_ep' references to an xarray per port Dan Williams
2022-06-29 17:19 ` Jonathan Cameron
2022-06-24 4:19 ` [PATCH 28/46] cxl/port: Move dport tracking to an xarray Dan Williams
2022-06-30 9:18 ` Jonathan Cameron
2022-07-10 19:06 ` Dan Williams
2022-06-24 4:19 ` [PATCH 29/46] cxl/port: Cache CXL host bridge data Dan Williams
2022-06-30 9:21 ` Jonathan Cameron
2022-07-10 19:09 ` Dan Williams
2022-06-24 4:19 ` [PATCH 30/46] cxl/hdm: Add sysfs attributes for interleave ways + granularity Dan Williams
2022-06-30 9:26 ` Jonathan Cameron
2022-07-10 20:40 ` Dan Williams
2022-07-19 14:32 ` Jonathan Cameron
2022-06-24 4:19 ` [PATCH 31/46] cxl/hdm: Initialize decoder type for memory expander devices Dan Williams
2022-06-30 9:33 ` Jonathan Cameron
2022-06-24 4:19 ` [PATCH 32/46] cxl/mem: Enumerate port targets before adding endpoints Dan Williams
2022-06-30 9:48 ` Jonathan Cameron
2022-07-10 21:01 ` Dan Williams
2022-06-24 4:19 ` [PATCH 33/46] resource: Introduce alloc_free_mem_region() Dan Williams
2022-06-30 10:35 ` Jonathan Cameron
2022-07-10 21:58 ` Dan Williams
2022-06-24 4:19 ` [PATCH 34/46] cxl/region: Add region creation support Dan Williams
2022-06-30 13:17 ` Jonathan Cameron
2022-07-11 0:08 ` Dan Williams
2022-07-19 14:42 ` Jonathan Cameron
2022-06-24 4:19 ` [PATCH 35/46] cxl/region: Add a 'uuid' attribute Dan Williams
2022-06-28 10:29 ` Jonathan Cameron
2022-06-28 14:24 ` Dan Williams
2022-06-24 4:19 ` [PATCH 36/46] cxl/region: Add interleave ways attribute Dan Williams
2022-06-30 13:44 ` Jonathan Cameron
2022-07-11 0:32 ` Dan Williams
2022-07-19 14:47 ` Jonathan Cameron [this message]
2022-07-19 22:15 ` Dan Williams
2022-07-20 9:59 ` Jonathan Cameron
2022-06-30 13:45 ` Jonathan Cameron
2022-06-24 4:19 ` [PATCH 37/46] cxl/region: Allocate host physical address (HPA) capacity to new regions Dan Williams
2022-06-30 13:56 ` Jonathan Cameron
2022-07-11 0:47 ` Dan Williams
2022-06-24 4:19 ` [PATCH 38/46] cxl/region: Enable the assignment of endpoint decoders to regions Dan Williams
2022-06-30 14:31 ` Jonathan Cameron
2022-07-11 1:12 ` Dan Williams
2022-06-24 4:19 ` [PATCH 39/46] cxl/acpi: Add a host-bridge index lookup mechanism Dan Williams
2022-06-30 15:48 ` Jonathan Cameron
2022-06-24 4:19 ` [PATCH 40/46] cxl/region: Attach endpoint decoders Dan Williams
2022-06-24 18:25 ` Jonathan Cameron
2022-06-24 18:49 ` Dan Williams
2022-06-24 20:51 ` Dan Williams
2022-06-24 23:21 ` Dan Williams
2022-06-30 16:34 ` Jonathan Cameron
2022-07-11 2:02 ` Dan Williams
2022-06-24 4:19 ` [PATCH 41/46] cxl/region: Program target lists Dan Williams
2022-06-24 4:19 ` [PATCH 42/46] cxl/hdm: Commit decoder state to hardware Dan Williams
2022-06-30 17:05 ` Jonathan Cameron
2022-07-11 3:02 ` Dan Williams
2022-06-24 4:19 ` [PATCH 43/46] cxl/region: Add region driver boiler plate Dan Williams
2022-06-30 17:09 ` Jonathan Cameron
2022-06-24 4:19 ` [PATCH 44/46] cxl/pmem: Delete unused nvdimm attribute Dan Williams
2022-06-30 17:10 ` Jonathan Cameron
2022-06-24 4:19 ` [PATCH 45/46] cxl/pmem: Fix offline_nvdimm_bus() to offline by bridge Dan Williams
2022-06-30 17:14 ` Jonathan Cameron
2022-07-11 19:49 ` Dan Williams
2022-06-24 4:19 ` [PATCH 46/46] cxl/region: Introduce cxl_pmem_region objects Dan Williams
2022-06-30 17:34 ` Jonathan Cameron
2022-07-11 20:05 ` Dan Williams
2022-06-24 15:13 ` [PATCH 00/46] CXL PMEM Region Provisioning Jonathan Cameron
2022-06-24 15:32 ` Dan Williams
2022-06-28 3:12 ` Alison Schofield
2022-06-28 3:34 ` Dan Williams
2022-07-02 2:26 ` Alison Schofield
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