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Current implementation of gettimex64() makes at least 3 PCIe reads to get current PHC time. It takes at least 2.2us to get this value back to userspace. At the same time there is cached value of upper bits of PHC available for packet timestamps already. This patch reuses cached value to speed up reading of PHC time. Signed-off-by: Vadim Fedorenko <vadfed@meta.com> Reviewed-by: Michael Chan <michael.chan@broadcom.com> Reviewed-by: Jacob Keller <jacob.e.keller@intel.com> Link: https://patch.msgid.link/20241114114820.1411660-1-vadfed@meta.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>