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Message-ID: <CAEz=LcutW6BZKB-Def3HmV=WrzjKjmAt_WnxPw3Yu45CoV0+Hw@mail.gmail.com>
Date: Sat, 10 May 2025 16:04:12 +0800
From: Greg Sword <gregsword0@...il.com>
To: Daisuke Matsuda <dskmtsd@...il.com>
Cc: Zhu Yanjun <yanjun.zhu@...ux.dev>, linux-kernel@...r.kernel.org,
linux-rdma@...r.kernel.org, leon@...nel.org, jgg@...pe.ca,
zyjzyj2000@...il.com
Subject: Re: [PATCH for-next v2 1/2] RDMA/rxe: Implement synchronous prefetch
for ODP MRs
On Sat, May 10, 2025 at 3:19 PM Daisuke Matsuda <dskmtsd@...il.com> wrote:
>
> On 2025/05/10 13:43, Zhu Yanjun wrote:
> >
> > 在 2025/5/10 4:46, Daisuke Matsuda 写道:
> >> On 2025/05/10 0:19, Zhu Yanjun wrote:
> >>> On 03.05.25 15:42, Daisuke Matsuda wrote:
> >>>> Minimal implementation of ibv_advise_mr(3) requires synchronous calls being
> >>>> successful with the IBV_ADVISE_MR_FLAG_FLUSH flag. Asynchronous requests,
> >>>> which are best-effort, will be added subsequently.
> >>>>
> >>>> Signed-off-by: Daisuke Matsuda <dskmtsd@...il.com>
> >>>> ---
> >>>> drivers/infiniband/sw/rxe/rxe.c | 7 +++
> >>>> drivers/infiniband/sw/rxe/rxe_loc.h | 10 ++++
> >>>> drivers/infiniband/sw/rxe/rxe_odp.c | 86 +++++++++++++++++++++++++++++
> >>>> 3 files changed, 103 insertions(+)
> >>>>
> >>>> diff --git a/drivers/infiniband/sw/rxe/rxe.c b/drivers/infiniband/sw/rxe/rxe.c
> >>>> index 3a77d6db1720..e891199cbdef 100644
> >>>> --- a/drivers/infiniband/sw/rxe/rxe.c
> >>>> +++ b/drivers/infiniband/sw/rxe/rxe.c
> >>>> @@ -34,6 +34,10 @@ void rxe_dealloc(struct ib_device *ib_dev)
> >>>> mutex_destroy(&rxe->usdev_lock);
> >>>> }
> >>>> +static const struct ib_device_ops rxe_ib_dev_odp_ops = {
> >>>> + .advise_mr = rxe_ib_advise_mr,
> >>>> +};
> >>>> +
> >>>> /* initialize rxe device parameters */
> >>>> static void rxe_init_device_param(struct rxe_dev *rxe, struct net_device *ndev)
> >>>> {
> >>>> @@ -103,6 +107,9 @@ static void rxe_init_device_param(struct rxe_dev *rxe, struct net_device *ndev)
> >>>> rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_SRQ_RECV;
> >>>> rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_FLUSH;
> >>>> rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_ATOMIC_WRITE;
> >>>> +
> >>>> + /* set handler for ODP prefetching API - ibv_advise_mr(3) */
> >>>> + ib_set_device_ops(&rxe->ib_dev, &rxe_ib_dev_odp_ops);
> >>>> }
> >>>> }
> >>>> diff --git a/drivers/infiniband/sw/rxe/rxe_loc.h b/drivers/infiniband/sw/rxe/rxe_loc.h
> >>>> index f7dbb9cddd12..21b070f3dbb8 100644
> >>>> --- a/drivers/infiniband/sw/rxe/rxe_loc.h
> >>>> +++ b/drivers/infiniband/sw/rxe/rxe_loc.h
> >>>> @@ -197,6 +197,9 @@ enum resp_states rxe_odp_atomic_op(struct rxe_mr *mr, u64 iova, int opcode,
> >>>> int rxe_odp_flush_pmem_iova(struct rxe_mr *mr, u64 iova,
> >>>> unsigned int length);
> >>>> enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr, u64 iova, u64 value);
> >>>> +int rxe_ib_advise_mr(struct ib_pd *pd, enum ib_uverbs_advise_mr_advice advice,
> >>>> + u32 flags, struct ib_sge *sg_list, u32 num_sge,
> >>>> + struct uverbs_attr_bundle *attrs);
> >>>> #else /* CONFIG_INFINIBAND_ON_DEMAND_PAGING */
> >>>> static inline int
> >>>> rxe_odp_mr_init_user(struct rxe_dev *rxe, u64 start, u64 length, u64 iova,
> >>>> @@ -225,6 +228,13 @@ static inline enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr,
> >>>> {
> >>>> return RESPST_ERR_UNSUPPORTED_OPCODE;
> >>>> }
> >>>> +static inline int rxe_ib_advise_mr(struct ib_pd *pd, enum ib_uverbs_advise_mr_advice advice,
> >>>> + u32 flags, struct ib_sge *sg_list, u32 num_sge,
> >>>> + struct uverbs_attr_bundle *attrs)
> >>>> +{
> >>>> + return -EOPNOTSUPP;
> >>>> +}
> >>>> +
> >>>> #endif /* CONFIG_INFINIBAND_ON_DEMAND_PAGING */
> >>>> #endif /* RXE_LOC_H */
> >>>> diff --git a/drivers/infiniband/sw/rxe/rxe_odp.c b/drivers/infiniband/sw/rxe/rxe_odp.c
> >>>> index 6149d9ffe7f7..e5c60b061d7e 100644
> >>>> --- a/drivers/infiniband/sw/rxe/rxe_odp.c
> >>>> +++ b/drivers/infiniband/sw/rxe/rxe_odp.c
> >>>> @@ -424,3 +424,89 @@ enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr, u64 iova, u64 value)
> >>>> return RESPST_NONE;
> >>>> }
> >>>> +
> >>>> +static int rxe_ib_prefetch_sg_list(struct ib_pd *ibpd,
> >>>> + enum ib_uverbs_advise_mr_advice advice,
> >>>> + u32 pf_flags, struct ib_sge *sg_list,
> >>>> + u32 num_sge)
> >>>> +{
> >>>> + struct rxe_pd *pd = container_of(ibpd, struct rxe_pd, ibpd);
> >>>> + unsigned int i;
> >>>> + int ret = 0;
> >>>> +
> >>>> + for (i = 0; i < num_sge; ++i) {
> >>>> + struct rxe_mr *mr;
> >>>> + struct ib_umem_odp *umem_odp;
> >>>> +
> >>>> + mr = lookup_mr(pd, IB_ACCESS_LOCAL_WRITE,
> >>>> + sg_list[i].lkey, RXE_LOOKUP_LOCAL);
> >>>> +
> >>>> + if (IS_ERR(mr)) {
> >>>> + rxe_dbg_pd(pd, "mr with lkey %x not found\n", sg_list[i].lkey);
> >>>> + return PTR_ERR(mr);
> >>>> + }
> >>>> +
> >>>> + if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_WRITE &&
> >>>> + !mr->umem->writable) {
> >>>> + rxe_dbg_mr(mr, "missing write permission\n");
> >>>> + rxe_put(mr);
> >>>> + return -EPERM;
> >>>> + }
> >>>> +
> >>>> + ret = rxe_odp_do_pagefault_and_lock(mr, sg_list[i].addr,
> >>>> + sg_list[i].length, pf_flags);
> >>>> + if (ret < 0) {
> >>>> + if (sg_list[i].length == 0)
> >>>> + continue;
> >>>> +
> >>>> + rxe_dbg_mr(mr, "failed to prefetch the mr\n");
> >>>> + rxe_put(mr);
> >>>> + return ret;
> >>>> + }
> >>>> +
> >>>> + umem_odp = to_ib_umem_odp(mr->umem);
> >>>> + mutex_unlock(&umem_odp->umem_mutex);
> >>>> +
> >>>> + rxe_put(mr);
> >>>> + }
> >>>> +
> >>>> + return 0;
> >>>> +}
> >>>> +
> >>>> +static int rxe_ib_advise_mr_prefetch(struct ib_pd *ibpd,
> >>>> + enum ib_uverbs_advise_mr_advice advice,
> >>>> + u32 flags, struct ib_sge *sg_list, u32 num_sge)
> >>>> +{
> >>>> + u32 pf_flags = RXE_PAGEFAULT_DEFAULT;
> >>>> +
> >>>> + if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH)
> >>>> + pf_flags |= RXE_PAGEFAULT_RDONLY;
> >>>> +
> >>>> + if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_NO_FAULT)
> >>>> + pf_flags |= RXE_PAGEFAULT_SNAPSHOT;
> >>>> +
> >>>> + /* Synchronous call */
> >>>> + if (flags & IB_UVERBS_ADVISE_MR_FLAG_FLUSH)
> >>>> + return rxe_ib_prefetch_sg_list(ibpd, advice, pf_flags, sg_list,
> >>>> + num_sge);
> >>>> +
> >>>> + /* Asynchronous call is "best-effort" */
> >>>
> >>> Asynchronous call is not implemented now, why does this comment appear?
> >>
> >> Even without the 2nd patch, async calls are reported as successful.
> >
> >
> > Async call is not implemented. How to call "async calls are reported as successful"?
>
> Please see the manual.
> cf. https://manpages.debian.org/testing/libibverbs-dev/ibv_advise_mr.3.en.html
>
> If IBV_ADVISE_MR_FLAG_FLUSH is not given to 'flags' parameter,
> then this function 'rxe_ib_advise_mr_prefetch()' simply returns 0.
> Consequently, ibv_advise_mr(3) and underlying ioctl(2) get no error.
> This behaviour is allowd in the spec as I quoted in the last reply.
The functionality wasn't implemented, you added the comments first.
You're still weaseling when people point this out.
>
> It might be nice to return -EOPNOTSUPP just below the comment instead,
> but not doing so is acceptable according to the spec. Additionally,
> such change will be overwritten in the next patch after all.
Move comments to the next patch. In this patch, return -EOPNOTSUPP.
--G--
>
> Thanks,
> Daisuke
>
> >
> >
> > Zhu Yanjun
> >
> >> The comment is inserted to show the reason, which is based on the
> >> description from 'man 3 ibv_advise_mr' as follows:
> >> ===
> >> An application may pre-fetch any address range within an ODP MR when using the IBV_ADVISE_MR_ADVICE_PREFETCH or IBV_ADVISE_MR_ADVICE_PREFETCH_WRITE advice. Semantically, this operation is best-effort. That means the kernel does not guarantee that underlying pages are updated in the HCA or the pre-fetched pages would remain resident.
> >> ===
> >>
> >> Thanks,
> >> Daisuke
> >>
> >>>
> >>> Zhu Yanjun
> >>>
> >>>> +
> >>>> + return 0;
> >>>> +}
> >>>> +
> >>>> +int rxe_ib_advise_mr(struct ib_pd *ibpd,
> >>>> + enum ib_uverbs_advise_mr_advice advice,
> >>>> + u32 flags,
> >>>> + struct ib_sge *sg_list,
> >>>> + u32 num_sge,
> >>>> + struct uverbs_attr_bundle *attrs)
> >>>> +{
> >>>> + if (advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH &&
> >>>> + advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_WRITE &&
> >>>> + advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_NO_FAULT)
> >>>> + return -EOPNOTSUPP;
> >>>> +
> >>>> + return rxe_ib_advise_mr_prefetch(ibpd, advice, flags,
> >>>> + sg_list, num_sge);
> >>>> +}
> >>>
> >>
>
>
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