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Several virtualization use-cases either don't support 32 MultiMSIs (Xen/VMware) or have significant drawbacks to their use (KVM's vIOMMU, which is required to support 32 MSI, needs to allocate an alternate system memory space for each device using vIOMMU (e.g. 8GB VM mem and 2 cards => 8 + 2 * 8 = 24GB host memory required)). Support these cases by enabling a 1 MSI fallback mode. Whenever all 32 MSIs requested are not available, a second request for a single MSI is made. Its success is the initiator of single MSI mode. This mode causes all interrupts generated by the device to be directed to the 0th MSI (firmware >=v1.10 will do this as a response to the PCIe MSI capability configuration). Likewise, all interrupt handlers for the device are registered to the 0th MSI. Since the DBC interrupt handler checks if the DBC is in use or if there is any pending changes, the 'spurious' interrupts are disregarded. If there is work to be done, the standard threaded IRQ handler is dispatched. On every interrupt, the MHI handler wakes up its threaded interrupt handler, and attempts to wake any waiters for MHI state events. Performance is within +-0.6% for test cases that typify real world use. Larger differences ([-4,+132]%, avg +47%) exist for very simple tasks (e.g. addition) compiled for single NSPs. It is assumed that the small work and many interrupts typically cause contention (e.g. 16 NSPs vs 4 CPUs), as evidenced by the standard deviation between runs also decreasing (r=-0.48 between delta(Performace_test) and delta(StdDev_test/Avg_test)) Signed-off-by: Carl Vanderlip <quic_carlv@quicinc.com> Reviewed-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@quicinc.com> Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com> Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com> Reviewed-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20231016170036.5409-1-quic_jhugo@quicinc.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.