在 2020/6/30 3:57, Raj, Ashok 写道: > Hi Bjorn > > > On Mon, Jun 29, 2020 at 02:33:16PM -0500, Bjorn Helgaas wrote: >> [+cc Ashok, Ding, Casey] >> >> On Mon, Jun 29, 2020 at 12:32:44PM +0300, Aya Levin wrote: >>> I wanted to turn on RO on the ETH driver based on >>> pcie_relaxed_ordering_enabled(). >>> From my experiments I see that pcie_relaxed_ordering_enabled() return true >>> on Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz. This CPU is from Haswell >>> series which is known to have bug in RO implementation. In this case, I >>> expected pcie_relaxed_ordering_enabled() to return false, shouldn't it? >> >> Is there an erratum for this? How do we know this device has a bug >> in relaxed ordering? > > https://software.intel.com/content/www/us/en/develop/download/intel-64-and-ia-32-architectures-optimization-reference-manual.html > > For some reason they weren't documented in the errata, but under > Optimization manual :-) > > Table 3-7. Intel Processor CPU RP Device IDs for Processors Optimizing PCIe > Performance > Processor CPU RP Device IDs > Intel Xeon processors based on Broadwell microarchitecture 6F01H-6F0EH > Intel Xeon processors based on Haswell microarchitecture 2F01H-2F0EH > > These are the two that were listed in the manual. drivers/pci/quirks.c also > has an eloborate list of root ports where relaxed_ordering is disabled. Did > you check if its not already covered here? > > Send lspci if its not already covered by this table. > Looks like the chip series is not in the errta list, but it is really difficult to distinguish and test. > >> >>> In addition, we are worried about future bugs in new CPUs which may result >>> in performance degradation while using RO, as long as the function >>> pcie_relaxed_ordering_enabled() will return true for these CPUs. >> >> I'm worried about this too. I do not want to add a Device ID to the >> quirk_relaxedordering_disable() list for every new Intel CPU. That's >> a huge hassle and creates a real problem for old kernels running on >> those new CPUs, because things might work "most of the time" but not >> always. > > I'll check when this is fixed, i was told newer ones should work properly. > But I'll confirm. > Maybe prevent the Relax Ordering for all Intel CPUs is a better soluton, looks like it will not break anything. Ding > > . >
