Re: [RFC V1 RESEND 0/6] Introduce dynamic allocation/freeing of MSI-X vectors
From: Bjorn Helgaas
Date: Thu Aug 01 2019 - 20:24:49 EST
On Fri, Jun 21, 2019 at 05:19:32PM -0700, Megha Dey wrote:
> Currently, MSI-X vector enabling and allocation for a PCIe device is
> static i.e. a device driver gets only one chance to enable a specific
> number of MSI-X vectors, usually during device probe. Also, in many
> cases, drivers usually reserve more than required number of vectors
> anticipating their use, which unnecessarily blocks resources that
> could have been made available to other devices. Lastly, there is no
> way for drivers to reserve more vectors, if the MSI-x has already been
> enabled for that device.
> Hence, a dynamic MSI-X kernel infrastructure can benefit drivers by
> deferring MSI-X allocation to post probe phase, where actual demand
> information is available.
> This patchset enables the dynamic allocation/de-allocation of MSI-X
> vectors by introducing 2 new APIs:
> pci_alloc_irq_vectors_dyn() and pci_free_irq_vectors_grp():
> We have had requests from some of the NIC/RDMA users who have lots of
> interrupt resources and would like to allocate them on demand,
> instead of using an all or none approach.
> The APIs are fairly well tested (multiple allocations/deallocations),
> but we have no early adopters yet. Hence, sending this series as an
> RFC for review and comments.
> The patches are based out of Linux 5.2-rc5.
> Megha Dey (6):
> PCI/MSI: New structures/macros for dynamic MSI-X allocation
> PCI/MSI: Dynamic allocation of MSI-X vectors by group
> x86: Introduce the dynamic teardown function
> PCI/MSI: Introduce new structure to manage MSI-x entries
If "entries" here means the same as "vectors" above, please use the
> PCI/MSI: Free MSI-X resources by group
Is "resources" the same as "vectors"?
> Documentation: PCI/MSI: Document dynamic MSI-X infrastructure
When you post a v2 after addressing Thomas' comments, please make
these subject lines imperative sentences beginning with a descriptive
verb. You can run "git log --oneline drivers/pci" to see the style.
If you're adding a specific interface or structure, mention it by name
in the subject if it's practical. The "x86" line needs a little more
context; I assume it should include "IRQ", "MSI-X", or something.
> Documentation/PCI/MSI-HOWTO.txt | 38 +++++
> arch/x86/include/asm/x86_init.h | 1 +
> arch/x86/kernel/x86_init.c | 6 +
> drivers/pci/msi.c | 363 +++++++++++++++++++++++++++++++++++++---
> drivers/pci/probe.c | 9 +
> include/linux/device.h | 3 +
> include/linux/msi.h | 13 ++
> include/linux/pci.h | 61 +++++++
> kernel/irq/msi.c | 34 +++-
> 9 files changed, 497 insertions(+), 31 deletions(-)