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[PATCH] crypto: fix bogus error benchmarking pbkdf on fast machines
https://lore.kernel.org/qemu-devel/[email protected] --- From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= <[email protected]> To: [email protected] Cc: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= <[email protected]>, Thomas Huth <[email protected]>, "Richard W.M. Jones" <[email protected]> Subject: [PATCH] crypto: fix bogus error benchmarking pbkdf on fast machines Date: Wed, 8 Jan 2025 18:43:54 +0000 Message-ID: <[email protected]> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; [email protected]; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.432, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: [email protected] X-Mailman-Version: 2.1.29 Precedence: list List-Id: <qemu-devel.nongnu.org> List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>, <mailto:[email protected]?subject=unsubscribe> List-Archive: <https://lists.nongnu.org/archive/html/qemu-devel> List-Post: <mailto:[email protected]> List-Help: <mailto:[email protected]?subject=help> List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>, <mailto:[email protected]?subject=subscribe> Errors-To: [email protected] Sender: [email protected] We're seeing periodic reports of errors like: $ qemu-img create -f luks --object secret,data=123456,id=sec0 \ -o key-secret=sec0 luks-info.img 1M Formatting 'luks-info.img', fmt=luks size=1048576 key-secret=sec0 qemu-img: luks-info.img: Unable to get accurate CPU usage This error message comes from a recent attempt to workaround a kernel bug with measuring rusage in long running processes: commit c72cab5 Author: Tiago Pasqualini <[email protected]> Date: Wed Sep 4 20:52:30 2024 -0300 crypto: run qcrypto_pbkdf2_count_iters in a new thread Unfortunately this has a subtle bug on machines which are very fast. On the first time around the loop, the 'iterations' value is quite small (1 << 15), and so will run quite fast. Testing has shown that some machines can complete this benchmarking task in as little as 7 milliseconds. Unfortunately the 'getrusage' data is not updated at the time of the 'getrusage' call, it is done asynchronously by the schedular. The 7 millisecond completion time for the benchmark is short enough that 'getrusage' sometimes reports 0 accumulated execution time. As a result the 'delay_ms == 0' sanity check in the above commit is triggering non-deterministically on such machines. The benchmarking loop intended to run multiple times, increasing the 'iterations' value until the benchmark ran for > 500 ms, but the sanity check doesn't allow this to happen. To fix it, we keep a loop counter and only run the sanity check after we've been around the loop more than 5 times. At that point the 'iterations' value is high enough that even with infrequent updates of 'getrusage' accounting data on fast machines, we should see a non-zero value. Reported-by: Thomas Huth <[email protected]> Reported-by: Richard W.M. Jones <[email protected]> Signed-off-by: Daniel P. Berrangé <[email protected]> --- crypto/pbkdf.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/crypto/pbkdf.c b/crypto/pbkdf.c index 0dd7c3aeaa..b285958319 100644 --- a/crypto/pbkdf.c +++ b/crypto/pbkdf.c @@ -107,7 +107,7 @@ static void *threaded_qcrypto_pbkdf2_count_iters(void *data) size_t nsalt = iters_data->nsalt; size_t nout = iters_data->nout; Error **errp = iters_data->errp; - + size_t scaled = 0; uint64_t ret = -1; g_autofree uint8_t *out = g_new(uint8_t, nout); uint64_t iterations = (1 << 15); @@ -131,7 +131,17 @@ static void *threaded_qcrypto_pbkdf2_count_iters(void *data) delta_ms = end_ms - start_ms; - if (delta_ms == 0) { /* sanity check */ + /* + * For very small 'iterations' values, CPU (or crypto + * accelerator) might be fast enough that the schedular + * hasn't incremented getrusage() data, or incremented + * it by a very small amount, resulting in delta_ms == 0. + * Once we've scaled 'iterations' x10, 5 times, we really + * should be seeing delta_ms != 0, so sanity check at + * that point. + */ + if (scaled > 5 && + delta_ms == 0) { /* sanity check */ error_setg(errp, "Unable to get accurate CPU usage"); goto cleanup; } else if (delta_ms > 500) { @@ -141,6 +151,7 @@ static void *threaded_qcrypto_pbkdf2_count_iters(void *data) } else { iterations = (iterations * 1000 / delta_ms); } + scaled++; } iterations = iterations * 1000 / delta_ms; -- 2.47.1 Signed-off-by: GitHub Actions Bot <[email protected]>
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