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References: <20220420191451.2904439-1-shr@fb.com> <20220420191451.2904439-7-shr@fb.com>
In-Reply-To: <20220420191451.2904439-7-shr@fb.com>
From: Kanchan Joshi <joshiiitr@gmail.com>
Date: Fri, 22 Apr 2022 06:55:49 +0530
Message-ID: <CA+1E3rKEr4ULc=065kRu_p1265vTE4x+0q+XNa49ie-YRXabdA@mail.gmail.com>
Subject: Re: [PATCH v2 06/12] io_uring: modify io_get_cqe for CQE32
To: Stefan Roesch <shr@fb.com>
Cc: io-uring@vger.kernel.org, kernel-team@fb.com
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On Thu, Apr 21, 2022 at 3:54 PM Stefan Roesch <shr@fb.com> wrote:
>
> Modify accesses to the CQE array to take large CQE's into account. The
> index needs to be shifted by one for large CQE's.
>
> Signed-off-by: Stefan Roesch <shr@fb.com>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
> fs/io_uring.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index c93a9353c88d..bd352815b9e7 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -1909,8 +1909,12 @@ static noinline struct io_uring_cqe *__io_get_cqe(struct io_ring_ctx *ctx)
> {
> struct io_rings *rings = ctx->rings;
> unsigned int off = ctx->cached_cq_tail & (ctx->cq_entries - 1);
> + unsigned int shift = 0;
> unsigned int free, queued, len;
>
> + if (ctx->flags & IORING_SETUP_CQE32)
> + shift = 1;
> +
> /* userspace may cheat modifying the tail, be safe and do min */
> queued = min(__io_cqring_events(ctx), ctx->cq_entries);
> free = ctx->cq_entries - queued;
> @@ -1922,12 +1926,13 @@ static noinline struct io_uring_cqe *__io_get_cqe(struct io_ring_ctx *ctx)
> ctx->cached_cq_tail++;
> ctx->cqe_cached = &rings->cqes[off];
> ctx->cqe_sentinel = ctx->cqe_cached + len;
> - return ctx->cqe_cached++;
> + ctx->cqe_cached++;
> + return &rings->cqes[off << shift];
> }
>
> static inline struct io_uring_cqe *io_get_cqe(struct io_ring_ctx *ctx)
> {
> - if (likely(ctx->cqe_cached < ctx->cqe_sentinel)) {
> + if (likely(ctx->cqe_cached < ctx->cqe_sentinel && !(ctx->flags & IORING_SETUP_CQE32))) {
> ctx->cached_cq_tail++;
> return ctx->cqe_cached++;
> }
This excludes CQE-caching for 32b CQEs.
How about something like below to have that enabled (adding
io_get_cqe32 for the new ring) -
+static noinline struct io_uring_cqe *__io_get_cqe32(struct io_ring_ctx *ctx)
+{
+ struct io_rings *rings = ctx->rings;
+ unsigned int off = ctx->cached_cq_tail & (ctx->cq_entries - 1);
+ unsigned int free, queued, len;
+
+ /* userspace may cheat modifying the tail, be safe and do min */
+ queued = min(__io_cqring_events(ctx), ctx->cq_entries);
+ free = ctx->cq_entries - queued;
+ /* we need a contiguous range, limit based on the current
array offset */
+ len = min(free, ctx->cq_entries - off);
+ if (!len)
+ return NULL;
+
+ ctx->cached_cq_tail++;
+ /* double increment for 32 CQEs */
+ ctx->cqe_cached = &rings->cqes[off << 1];
+ ctx->cqe_sentinel = ctx->cqe_cached + (len << 1);
+ return ctx->cqe_cached;
+}
+
+static inline struct io_uring_cqe *io_get_cqe32(struct io_ring_ctx *ctx)
+{
+ struct io_uring_cqe *cqe32;
+ if (likely(ctx->cqe_cached < ctx->cqe_sentinel)) {
+ ctx->cached_cq_tail++;
+ cqe32 = ctx->cqe_cached;
+ } else
+ cqe32 = __io_get_cqe32(ctx);
+ /* double increment for 32b CQE*/
+ ctx->cqe_cached += 2;
+ return cqe32;
+}