From: Dan Williams <dan.j.williams@intel.com> To: Jeff Moyer <jmoyer@redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, Michael Ellerman <mpe@ellerman.id.au>, linux-nvdimm <linux-nvdimm@lists.01.org>, alistair@popple.id.au, Mikulas Patocka <mpatocka@redhat.com> Subject: Re: [PATCH v2 3/5] libnvdimm/nvdimm/flush: Allow architecture to override the flush barrier Date: Thu, 21 May 2020 11:34:08 -0700 [thread overview] Message-ID: <CAPcyv4hbwqrERcs4oVGOAnew0A=HRm0muoKm3+4UzZLpOF12Yw@mail.gmail.com> (raw) In-Reply-To: <x49o8qh9wu5.fsf@segfault.boston.devel.redhat.com> On Thu, May 21, 2020 at 7:39 AM Jeff Moyer <jmoyer@redhat.com> wrote: > > Dan Williams <dan.j.williams@intel.com> writes: > > >> But I agree with your concern that if we have older kernel/applications > >> that continue to use `dcbf` on future hardware we will end up > >> having issues w.r.t powerfail consistency. The plan is what you outlined > >> above as tighter ecosystem control. Considering we don't have a pmem > >> device generally available, we get both kernel and userspace upgraded > >> to use these new instructions before such a device is made available. > > I thought power already supported NVDIMM-N, no? So are you saying that > those devices will continue to work with the existing flushing and > fencing mechanisms? > > > Ok, I think a compile time kernel option with a runtime override > > satisfies my concern. Does that work for you? > > The compile time option only helps when running newer kernels. I'm not > sure how you would even begin to audit userspace applications (keep in > mind, not every application is open source, and not every application > uses pmdk). I also question the merits of forcing the administrator to > make the determination of whether all applications on the system will > work properly. Really, you have to rely on the vendor to tell you the > platform is supported, and at that point, why put further hurdles in the > way? I'm thoroughly confused by this. I thought this was exactly the role of a Linux distribution vendor. ISVs qualify their application on a hardware-platform + distribution combination and the distribution owns picking ABI defaults like CONFIG_SYSFS_DEPRECATED regardless of whether they can guarantee that all apps are updated to the new semantics. The administrator is not forced, the administrator if afforded an override in the extreme case that they find an exception to what was qualified and need to override the distribution's compile-time choice. > > The decision to require different instructions on ppc is unfortunate, > but one I'm sure we have no control over. I don't see any merit in the > kernel disallowing MAP_SYNC access on these platforms. Ideally, we'd > have some way of ensuring older kernels don't work with these new > platforms, but I don't think that's possible. I see disabling MAP_SYNC as the more targeted form of "ensursing older kernels don't work. So I guess we agree that something should break when baseline assumptions change, we just don't yet agree on where that break should happen? _______________________________________________ Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org To unsubscribe send an email to linux-nvdimm-leave@lists.01.org
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From: Dan Williams <dan.j.williams@intel.com> To: Jeff Moyer <jmoyer@redhat.com> Cc: linux-nvdimm <linux-nvdimm@lists.01.org>, "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>, Mikulas Patocka <mpatocka@redhat.com>, alistair@popple.id.au, linuxppc-dev <linuxppc-dev@lists.ozlabs.org> Subject: Re: [PATCH v2 3/5] libnvdimm/nvdimm/flush: Allow architecture to override the flush barrier Date: Thu, 21 May 2020 11:34:08 -0700 [thread overview] Message-ID: <CAPcyv4hbwqrERcs4oVGOAnew0A=HRm0muoKm3+4UzZLpOF12Yw@mail.gmail.com> (raw) In-Reply-To: <x49o8qh9wu5.fsf@segfault.boston.devel.redhat.com> On Thu, May 21, 2020 at 7:39 AM Jeff Moyer <jmoyer@redhat.com> wrote: > > Dan Williams <dan.j.williams@intel.com> writes: > > >> But I agree with your concern that if we have older kernel/applications > >> that continue to use `dcbf` on future hardware we will end up > >> having issues w.r.t powerfail consistency. The plan is what you outlined > >> above as tighter ecosystem control. Considering we don't have a pmem > >> device generally available, we get both kernel and userspace upgraded > >> to use these new instructions before such a device is made available. > > I thought power already supported NVDIMM-N, no? So are you saying that > those devices will continue to work with the existing flushing and > fencing mechanisms? > > > Ok, I think a compile time kernel option with a runtime override > > satisfies my concern. Does that work for you? > > The compile time option only helps when running newer kernels. I'm not > sure how you would even begin to audit userspace applications (keep in > mind, not every application is open source, and not every application > uses pmdk). I also question the merits of forcing the administrator to > make the determination of whether all applications on the system will > work properly. Really, you have to rely on the vendor to tell you the > platform is supported, and at that point, why put further hurdles in the > way? I'm thoroughly confused by this. I thought this was exactly the role of a Linux distribution vendor. ISVs qualify their application on a hardware-platform + distribution combination and the distribution owns picking ABI defaults like CONFIG_SYSFS_DEPRECATED regardless of whether they can guarantee that all apps are updated to the new semantics. The administrator is not forced, the administrator if afforded an override in the extreme case that they find an exception to what was qualified and need to override the distribution's compile-time choice. > > The decision to require different instructions on ppc is unfortunate, > but one I'm sure we have no control over. I don't see any merit in the > kernel disallowing MAP_SYNC access on these platforms. Ideally, we'd > have some way of ensuring older kernels don't work with these new > platforms, but I don't think that's possible. I see disabling MAP_SYNC as the more targeted form of "ensursing older kernels don't work. So I guess we agree that something should break when baseline assumptions change, we just don't yet agree on where that break should happen?
next prev parent reply other threads:[~2020-05-21 18:34 UTC|newest] Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-05-13 3:47 [PATCH v2 1/5] powerpc/pmem: Add new instructions for persistent storage and sync Aneesh Kumar K.V 2020-05-13 3:47 ` Aneesh Kumar K.V 2020-05-13 3:47 ` [PATCH v2 2/5] powerpc/pmem: Add flush routines using new pmem store and sync instruction Aneesh Kumar K.V 2020-05-13 3:47 ` Aneesh Kumar K.V 2020-05-13 3:47 ` [PATCH v2 3/5] libnvdimm/nvdimm/flush: Allow architecture to override the flush barrier Aneesh Kumar K.V 2020-05-13 3:47 ` Aneesh Kumar K.V 2020-05-13 16:14 ` Dan Williams 2020-05-13 16:14 ` Dan Williams 2020-05-19 5:30 ` Aneesh Kumar K.V 2020-05-19 5:30 ` Aneesh Kumar K.V 2020-05-19 7:09 ` Dan Williams 2020-05-19 7:09 ` Dan Williams 2020-05-19 13:52 ` Aneesh Kumar K.V 2020-05-19 13:52 ` Aneesh Kumar K.V 2020-05-19 18:59 ` Dan Williams 2020-05-19 18:59 ` Dan Williams 2020-05-20 18:43 ` Aneesh Kumar K.V 2020-05-20 18:43 ` Aneesh Kumar K.V 2020-05-21 14:38 ` Jeff Moyer 2020-05-21 14:38 ` Jeff Moyer 2020-05-21 17:02 ` Aneesh Kumar K.V 2020-05-21 17:02 ` Aneesh Kumar K.V 2020-05-21 18:25 ` Dan Williams 2020-05-21 18:25 ` Dan Williams 2020-05-21 18:52 ` Mikulas Patocka 2020-05-21 18:52 ` Mikulas Patocka 2020-05-22 9:31 ` Michal Suchánek 2020-05-22 9:31 ` Michal Suchánek 2020-05-22 10:08 ` Aneesh Kumar K.V 2020-05-22 10:08 ` Aneesh Kumar K.V 2020-05-22 13:01 ` Mikulas Patocka 2020-05-22 13:01 ` Mikulas Patocka 2020-06-26 10:20 ` Michal Suchánek 2020-06-26 10:20 ` Michal Suchánek 2020-05-21 18:34 ` Dan Williams [this message] 2020-05-21 18:34 ` Dan Williams 2020-05-13 3:47 ` [PATCH v2 4/5] powerpc/pmem/of_pmem: Update of_pmem to use the new barrier instruction Aneesh Kumar K.V 2020-05-13 3:47 ` Aneesh Kumar K.V 2020-05-13 6:44 ` kbuild test robot 2020-05-13 6:44 ` kbuild test robot 2020-05-13 6:44 ` kbuild test robot 2020-05-13 3:47 ` [PATCH v2 5/5] powerpc/pmem: Avoid the barrier in flush routines Aneesh Kumar K.V 2020-05-13 3:47 ` Aneesh Kumar K.V
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