Re: [PATCH v3 08/12] io_uring: overflow processing for CQE32

[Kanchan Joshi <joshi.k@samsung.com>]

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On Mon, Apr 25, 2022 at 11:25:26AM -0700, Stefan Roesch wrote:
>This adds the overflow processing for large CQE's.
>
>This adds two parameters to the io_cqring_event_overflow function and
>uses these fields to initialize the large CQE fields.
>
>Allocate enough space for large CQE's in the overflow structue. If no
>large CQE's are used, the size of the allocation is unchanged.
>
>The cqe field can have a different size depending if its a large
>CQE or not. To be able to allocate different sizes, the two fields
>in the structure are re-ordered.
>
>Co-developed-by: Jens Axboe <axboe@kernel.dk>
>Signed-off-by: Stefan Roesch <shr@fb.com>
>Signed-off-by: Jens Axboe <axboe@kernel.dk>
>---
> fs/io_uring.c | 31 ++++++++++++++++++++++---------
> 1 file changed, 22 insertions(+), 9 deletions(-)
>
>diff --git a/fs/io_uring.c b/fs/io_uring.c
>index 68b61d2b356d..3630671325ea 100644
>--- a/fs/io_uring.c
>+++ b/fs/io_uring.c
>@@ -220,8 +220,8 @@ struct io_mapped_ubuf {
> struct io_ring_ctx;
>
> struct io_overflow_cqe {
>-	struct io_uring_cqe cqe;
> 	struct list_head list;
>+	struct io_uring_cqe cqe;
> };
>
> struct io_fixed_file {
>@@ -2017,10 +2017,14 @@ static void io_cqring_ev_posted_iopoll(struct io_ring_ctx *ctx)
> static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force)
> {
> 	bool all_flushed, posted;
>+	size_t cqe_size = sizeof(struct io_uring_cqe);
>
> 	if (!force && __io_cqring_events(ctx) == ctx->cq_entries)
> 		return false;
>
>+	if (ctx->flags & IORING_SETUP_CQE32)
>+		cqe_size <<= 1;
>+
> 	posted = false;
> 	spin_lock(&ctx->completion_lock);
> 	while (!list_empty(&ctx->cq_overflow_list)) {
>@@ -2032,7 +2036,7 @@ static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force)
> 		ocqe = list_first_entry(&ctx->cq_overflow_list,
> 					struct io_overflow_cqe, list);
> 		if (cqe)
>-			memcpy(cqe, &ocqe->cqe, sizeof(*cqe));
>+			memcpy(cqe, &ocqe->cqe, cqe_size);

Maybe a nit, but if we do it this way -
memcpy(cqe, &ocqe->cqe, 
	sizeof(*cqe) << (ctx->flags & IORING_SETUP_CQE32));

we can do away with all previous changes in this function.


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