From 23e967e17c58779b38f69f8d41d727f59440d36a Mon Sep 17 00:00:00 2001 From: Tom Lendacky Date: Mon, 5 Jun 2017 14:52:26 -0500 Subject: [PATCH] iommu/amd: Reduce delay waiting for command buffer space Currently if there is no room to add a command to the command buffer, the driver performs a "completion wait" which only returns when all commands on the queue have been processed. There is no need to wait for the entire command queue to be executed before adding the next command. Update the driver to perform the same udelay() loop that the "completion wait" performs, but instead re-read the head pointer to determine if sufficient space is available. The very first time it is found that there is no space available, the udelay() will be skipped to immediately perform the opportunistic read of the head pointer. If it is still found that there is not sufficient space, then the udelay() will be performed. Signed-off-by: Leo Duran Signed-off-by: Tom Lendacky Signed-off-by: Joerg Roedel --- drivers/iommu/amd_iommu.c | 33 +++++++++++++-------------------- 1 file changed, 13 insertions(+), 20 deletions(-) diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c index d81c895ff4f4..1efbef7f3b61 100644 --- a/drivers/iommu/amd_iommu.c +++ b/drivers/iommu/amd_iommu.c @@ -1045,7 +1045,7 @@ static int __iommu_queue_command_sync(struct amd_iommu *iommu, struct iommu_cmd *cmd, bool sync) { - bool read_head = true; + unsigned int count = 0; u32 left, next_tail; next_tail = (iommu->cmd_buf_tail + sizeof(*cmd)) % CMD_BUFFER_SIZE; @@ -1053,33 +1053,26 @@ again: left = (iommu->cmd_buf_head - next_tail) % CMD_BUFFER_SIZE; if (left <= 0x20) { - struct iommu_cmd sync_cmd; - int ret; - - if (read_head) { - /* Update head and recheck remaining space */ - iommu->cmd_buf_head = readl(iommu->mmio_base + - MMIO_CMD_HEAD_OFFSET); - read_head = false; - goto again; - } - - read_head = true; - - iommu->cmd_sem = 0; + /* Skip udelay() the first time around */ + if (count++) { + if (count == LOOP_TIMEOUT) { + pr_err("AMD-Vi: Command buffer timeout\n"); + return -EIO; + } - build_completion_wait(&sync_cmd, (u64)&iommu->cmd_sem); - copy_cmd_to_buffer(iommu, &sync_cmd); + udelay(1); + } - if ((ret = wait_on_sem(&iommu->cmd_sem)) != 0) - return ret; + /* Update head and recheck remaining space */ + iommu->cmd_buf_head = readl(iommu->mmio_base + + MMIO_CMD_HEAD_OFFSET); goto again; } copy_cmd_to_buffer(iommu, cmd); - /* We need to sync now to make sure all commands are processed */ + /* Do we need to make sure all commands are processed? */ iommu->need_sync = sync; return 0; -- 2.20.1